You could try this :
"1. Remove the leg that is the battery compartment cover. Under this are two small screws. Remove them as well.
2. On the other leg is a plastic plug that covers a critical screw- it has to come out. I ended up prying it out with a small screwdriver, marring the plastic around it and destroying the plug in the process. Once I got it out, I did not see any way I could have done it differently, but the plug was mangled enough that I might have been missing something.
3. Once the plug is out, remove the exposed screw and remove this leg about the same way the battery leg comes off. Note that it sort of has to snap in and out of place. Just be careful not to break the snap.
4. Remove the two screws exposed in it's rear.
5. Remove the two screws under the neck and carefully ease the body apart. It will hang up a little on the speaker jack- just ease it past that."
A picture tutorila for the hasbro dissection is here http://ctrlsave.com/airmonsters/?page_id=131&paged=3
Here is some stuff on the Sega iDog http://home.comcast.net/~botsmaker/idog.html
Hope this helps to get the puppy barking again.....;-)