any way to get cats from joining parcels to share territory?

[Tad Carlucci]

Lag as you're describing ("rubber-banding") is not possible. It arises from network lag and your viewer incorrectly predicting the future location of a moving object. The cat might appear, on your screen, but only on your screen, to leave the area but when your view catches up the cat will snap back.

The problem with fences and floors is that cats change from physical to non-physical and move their center a bit as they sleep, sit, stretch, etc. Basically, the wall/floor occasionally disappears and they walk through it (not as-if, but literally because, it is not there).

Setting your cat to sim range (or any large range) and using walls and floors to keep it in an area will usually work. But it won't always work.

Your best bet is to home the cat at the mid-point and set a range which does not extend beyond the parcel(s) in question.