any ideas on how to keep my cat from going out my doggie door??

Some good answers ahead of me--but remember--cats hate

"citrus"--U can put orange peels near the doggie door and the cat will not go close--also stay off furniture,etc . There are also

commercial sprays (lemon , orange, etc) available at ALL pet stores..Just spritz a little in the area U want your cat to stay away from and VOILA. The "scent" is pleasant to humans, and non-toxic, but cats just hate it.

cats don't like aluminum foil. Either hang an aluminum pie tray (the cheap disposable kind you buy at the grocery store) beside the door or put heavy duty aluminum foil around the door. If they step on it or hear the sound it makes, they should turn and go the other way.

Get the one with the magnet controlled thing on the collar!!! Only give the dog the collar.

sit on the outside and wait for him to come out, have a squirt gun ready and zap him with it everytime he sticks his head out. Do this a few times and he will stop,

lock the door and train your dog to bark wen it wants to go outside