A friend of mine who is studying to be a vet just told me that I can have an electric fence put in, and what matters is the strength of the collar put on the animal. So I can put collars of a different level onto my cats than I do the larger dog.
This is interesting. My neighbours have two, well one now, small Beagle size dog and she is contained by the invisible fence. Apparently they cannot make it strong enough to also contain their Bullmastiff so she has to stay in the house. The Bullmastiff doesn't seem to even know there is a fence, she has no reaction at all. Do you know what brand it is that allows you to vary the strength by the collar?
Just to add, the fence does not keep other animals out and when we came back from a bike ride yesterday my dog went over for a visit and then both dogs, even the small one, were lured out by mine, zap or not.