We had the same problem with our puppy. He'd shred the pad and then have an accident. We tried double-sided tape, but that didn't work. We got one of these:
PetEdge: Clean Go Pet Puppy Pad Holder
These do a great job of getting the pads to stay put. At first, he actually unhinged the handles and pulled the holder apart to get at the puppy pad. Then I put some tabasco sauce on the handles so he couldn't any longer. Since then, he's gone on his pad and he hasn't played with it at all.