Originally Posted by cmeghna
Thanks so much to everyone for their advice.
I do need to clarify something, though (sorry, I obviously wasn't as clear before as I meant to be): I really don't mean for the cats to go outside at all unless it's with a harness and leash on in the backyard when someone else is there. My problem is that they lie in wait and dart out the door when you open it, either to go out yourself or for someone to come in. We're usually really good about commanding them (insofar as cats can be commanded) to stay put or by blocking the space with a foot, but every so often they do manage to scramble out, or a visitor accidentally leaves the door open.
They're both also really good jumpers: I've seen them do a standing 5.5 foot jump: scared the living daylights out of me! So I don't imagine the baby gate will work, unfortunately.
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. I'm hoping this will work, and will return and post again with what I find.
PS: there's no back door: there is a side door, but it doesn't lead to the backyard. We actually have to take a little path to get to the back yard from the side door!
One thing before you put in this electric fence. Can you try out the collars on yourself? What will work with your dog won't work for your cats. It will be too strong and may kill them. If it is an electric fence per se you can not adjust strengths. Then you will be able to see what the animal will feel like to have that done to them.
As others have told you - the zap getting through the fence probably won't stop them from getting out if they see something they want to go after. It will
make them hesitate to come back.
There are many ideas out there that will work to keep your cats in. Maybe you can build a small enclosed porch on the side of the house so people have to come in there and one door is closed before the other to your home is opened. If you rent it is as simple as putting up a "room" of posts and chicken wire so if kitties run out you can have time to grab them and put them back in. If it is completely closed off, even the top, cats can't get out. May not be attractive, although you can make it so, but it would be very effective. Just a thought.