How to keep dogs/cats out of yard?

There are motion activated water sprays you can get but depending on your yard size you may need more than one. There are also mild electronic shock fences you can get.

Sprinkle cayenne pepper, chili powder around the areas they are going to. One sniff and they will remember. May need to apply a few times until they learn.

I have heard moth balls and rosemary plants keep them out of your yards.

If it's dogs, look to see where they are getting in. Dogs will generally poop on the ground. Cats will usually bury it. If you find poop buried in sand/loose soil, it's cats. If it does turn out to be cats, you can try wolf urine scent (stronger predator scent will usually scare off most animals) although the motion detection water spray suggested by Dave will probably work better. If it's a dog, you likely have a hole under/in your fence. Best thing to do is to find the hole(s) and fix.

It's amazing how animals can get through fences that look impenetrable. I can't figure out how rabbits, etc. get into fenced yards that g down to soil level. Our dogs usually take care of them for us.

Cayenne pepper where they have messed in your yard. You have to apply it after heavy dew or rain. DO NOT use if children play in the yard. I use it on porch steps to keep feral cats aways.

find out how they are getting in and repair the fence; if you have a local "Animal Control' they can set humane (box) traps for them. See if you can determine why they want to come into your yard -- food ?? Something has to be attracting them.