ARGGGGHHH, had a response all typed, was doing a correction and hit a button, don't know what one, and went from here to another area, so lost it all.
Okay, shorter version, in the guide there is the cheats info on how to do the buydebug, the steps needed to get to it, and you have to go through edit town. I don't know what you (Anna33) know so I won't try (this time) to give the steps. I have checked and there are no spawners for rodents anywhere on the lot. So, that can't be the reason.
I have a Boney in every game and she has a thing for raking leaves, and I have lots of trees, flowers, rocks, a pond, and other items for my landscaping, so I guess that explains why the critters.
On the bright side, my family can go and catch the critters and get some money for them, compensation for the aggrevation of them.