Greg Jessup likes to squeeze money out of his five-bedroom house in Wilton, Conn., wherever possible, frequently listing it on Airbnb. But this spring, he took a good look at the space around the house and saw its potential, too.

In May, he began listing the manicured grounds on Sniffspot, an app where homeowners rent out their yards by the hour to dog owners in search of fenced-in spaces where their pooches can play. “I’m always looking for any way to make an extra few bucks,” said Mr. Jessup, 43, a chief technology officer for a hedge fund, who charges guests $8 an hour for use of the space, and subsequently listed his swimming pool on a pool rental app, too. “If someone is going to give me a few bucks to use the yard, great.”

Sniffspot is among the latest start-ups designed to help homeowners capitalize on every inch of their properties. While vacation apps like Airbnb and Vrbo have long dominated the market with conventional home rentals, newer ones have crashed the party with specialized offerings — like Swimply, where homeowners rent out their pools by the hour, and Splacer and Peerspace, which turn living rooms into party venues. The uses vary, but the underlying concept is the same: A homeowner creates a profile on an app, uploads a few photographs, and presumably the bookings roll in.

Sniffspot started in Seattle in 2018 as a simple website. Now based in Boston, the company is in 1,500 cities, with 7,000 hosts logging about 10,000 bookings a month, according to David Adams, 35, the company’s founder. Guests log on, look for locations near their home, and sign up, with most listings priced at around $10 an hour for one dog or $15 for two.

Averaging about three to four guests a week, Mr. Jessup’s profit is modest after he pays the 22 percent commission that Sniffspot shaves off the top, plus the credit card processing fee. But as far as passive income goes, it doesn’t get much easier than hosting dogs. Mr. Jessup simply leaves guests a key to the backyard, and they come and go without any effort on his part. “Literally, I do nothing,” he said. “We have a hose.”

Some hosts are more involved, like Meghan Rabon, who rents out her acre lot in Oxford, N.J., a rural community of 2,500 people about 70 miles west of New York City. “We make it a doggie paradise,” said Ms. Rabon, 37, standing in her backyard one recent Saturday. The shaded, fenced yard has a small aboveground pool with a ramp so the dogs can jump in. At the bottom of a long, gentle slope is an obstacle course with a seesaw, tunnels and puppy parkour equipment designed to exhaust any four-legged visitor. The day I visited, the birds chirped, a rooster crowed from a nearby property, and my dog was in heaven, bolting from one end of the fenced property to the other.

Ms. Rabon, who breeds Jack Russell Terriers and works for a pharmaceutical lab, said most of her guests drive from New York City in search of space for their apartment-bound pups. I paid $35 for an hourlong visit, a premium for the site, but Ms. Rabon said she keeps the price high to limit usage since each booking means she may have to mow the lawn, clean the pool and tidy the equipment.

My dog had little interest in the agility course with hoops and poles to jump. He only wanted to play fetch with a squeaky, pink plastic hippo that he found in a bucket. But I imagined that if Ms. Rabon were located close enough for regular visits, I might put the effort into training him to do circus acts.

Sniffspot positions itself as an alternative to the local dog park or even the leisurely walk. For skittish or anxious dogs, playing with other dogs can be stressful and unpleasant. For a few dollars, a devoted pet owner can secure a private dog park and expose a bored pooch to new scents and experiences. “It’s very enriching for a dog to be in a new place,” Mr. Adams said.

The biggest challenge many users face is actually finding a Sniffspot to use. Availability is still inconsistent, and concentrated in Seattle, where the company started (a quarter of all bookings are in Washington State). Growth had “been purely word of mouth, organic growth, it’s just something that people need,” Mr. Adams said, adding. “To say these things take off like a rocket, that’s not actually how these things happen.”

But for dog owners like Genie Leslie, 34, a copywriter and screenwriter in Seattle, Sniffspot has become a regular routine. Ms. Leslie lives in a townhouse with no yardspace for her dog, Darcy, to run around. Darcy, a rescue, is reactive around people and other dogs, often making the afternoon walk a stressful grind.

Hanging out in someone else’s yard “is honestly more relaxing for us than being out with her on-leash, because we don’t have to manage her reactions,” Ms. Leslie said. Recently she found a 10-acre location about 40 minutes away. At $20 an hour, she and Darcy make the trek once a month for a two-hour visit. “She can run, play, test out some basic agility equipment, and even stick her paws in a creek,” she said.

Renting your property to an endless rotation of visitors is not without its pitfalls. Last year, one guest who booked Ms. Rabon’s property brought the dog — and seven human guests. The group blasted music, ordered delivery food and overstayed their visit by nearly an hour. When Ms. Rabon finally asked them to go, they left behind all their trash. “They were looking for a place to party,” she said.

Sniffspot banned the user in response, according to Ms. Rabon. But she was so rattled by the experience that she stopped listing her space for the rest of the season, only reopening it this month. Other hosts have complained about guests who fail to pick up after their dogs, park cars in the wrong spots or complain about a host’s political signage.

But for a job that, for the most part, involves little more than leaving out a bowl of water, most homeowners seem content. Nandini Persaud, 43, who lives in the Bronx and rents out her small yard, said she sometimes comes home and realizes that her property was visited while she was gone because items have been moved around.

So what’s it like to have random people wander through your yard? Ask Stacy Couch. She’s had more than 1,000 bookings since February 2021, when she first listed her five-acre property outside Minneapolis. Sniffspot users have unfettered access to about three of the forested acres, with walking trails. Ms. Couch, 56, who owned a housecleaning service before she retired, says business is so busy in the warmer months that she has to block off times for herself. With 30 to 40 bookings a week, she would never get to tramp around her own land with her dogs, or forage the black raspberries that grow in the summer.

So she clears an hour a day for her own dogs. “My guys, they like it out there, too,” she said. But on the day we spoke, they’d missed their scheduled 11 a.m. romp. “I think tonight after 8 is open.”