At 4 months, and the few prior, our GSP has destroyed anything that squeaks, including attempts at the cat. (cat fights back) These toys are favorites of his also, and when he goes in the back yard to do his business, you can tell by visual inspection when he has been on a steady diet of cotton stuffing to supplement his food.
"
Kong" toys or similar, freeze with a little peanut butter I'm told is a good way to keep 'em busy. We have a "Buster Box" which is a puzzle box for their dogfood, that they have to knock around to get the food out, and it comes out really slowly. That buster box keeps him busiest the longest. We probably feed half his food to him that way. Its all but indestructible by a dog. Hard, slick plastic, with no angles acute enough for them to get their mouth around.