Just get one of these:
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I take it that kindly asking the pet owners to keep their pets off your property would only open up a can of angry worms. It's funny how responsible people are considered the bad guy in these situations whereas those not abiding by local ordinances do things at the expense of others and feel like it's okay. Or perhaps you have feral cats and dogs running loose. I hate to be that old guy shaking my fist and yelling "get off my lawn" but damn, why can't people be respectful of other people's property?
I have one of these signs in my yard but people are so dumb they read it to mean that it's acceptable to have dogs urinate on the lawn. If you see a sign like this then probably be best just to take your dog elsewhere. People are so stupid!!
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As a matter of fact my yard became a zoo, seriously.
There are pet owners who are lazy to take their dog for a walk, so they release them in early morning: 3:00 to 5:00 am or in other hours where they assume people will not notice or be home.
One of the dog found my yard as inviting place and made it its constant place, i'm too lazy to plan a stakeout, the dog doesn't come every night, it usually comes 3 nights a week.
Other unleashed dogs, also visit, probably follow the smell.
There is no real enforcement in my city of many rules, let a lone pet related.
Also, there are coyote that pass in the yard, but they are cat/dog friendly, they only eat dead animals or leftovers.
Also, there are also a few porcupines who made my yard part of their path for finding food.
There are many stray cats who visit the yard and find it nice, since it has a lot of sand and sun.
The coyotes and porcupines come from a nearby park.