We live in a very friendly neighborhood and love almost all of our neighbors.
However

, we have one family that freely (without asking) is continually coming through our fence and hanging out in out backyard. I've glanced up from my kitchen and there one is looking at me from my back patio.
We do have a fence--doesn't matter. This is also a family that we are not as close to and they have never invited a single other family to their home. Conversely- they have been to quite a few events at our house which makes it even more annoying. Its been a few years too. I've never seen the inside of their house. They have never hosted and everyone else in the neighbirhoid routinely does.
My kid are much older--elementary school. They have an infant and toddler.
We just redid our entire backyard and it is very nice back there. If I am hanging out with my own kids --they'll just come through the gate and not leave.
I grew up in a house with a yard and the unspoken KNOWN rule is you don't go in other peoples yards (especially through a back fence) unless you are invited--or at the very least we are there. I am totally fine with kids retrieving balls, etc. my own kids friends will come over when they hear my kids and that's fine too.
But adults/families just using my yard like it's their own- not ok. We also have a fantastic neighbirhood park that is filled with kids their age yet they seem to never go there and prefer to use my yard for personal enjoyment.
So since they aren't listening--wtf do I do?