My Savanna is being polluted by stupid people

It all happened yesterday when I took my dogs for their evening walks. I usually don't take them too far. I let them loose on our own property, the part that is still left wild. I call this part the savanna because, well it looks like a savanna minus the lion, zebras and giraffes of course!

So, coming back to yesterday, I was really angry to see that some people have dumped their garbage on our land. I just can't imagine how someone could make so much effort just to dump his garbage in the property of others when in this region scavengers make rounds twice a week! Instead of dumping the trash here, they could just have put them in those big LMLC sacks and waited patiently for the scavengers to come and collect them. Duh! They must have looked really stupid taking all their garbage presumably by night and coming to dump them here.

My mother's take on this is that those people are not aware that scavengers do collect plastic stuff and they thought they cannot burn their garbage either so they just carried the whole of them and came to dump them here with the hope that the land owner will not notice the huge pile of garbage.

I'm still figuring out what to do about this. My father suggested a "private property, do not dump" sort of sign to be put there.

Do you think this can solve the problem?