I have a hard time even when i buy the tough toys. my lab will get jealous sometimes and destroy things. she actually tore up a kong stick that i had for edgar (who loved it). i thought edgar was just overzealous. nope, it was ganja!
my adv is to buy toys that don't look like much of anything. check and see how the ears and eyes are sewn on, almost like you would for a human child. if it has a tail or ears, the dogs go straight for that. i think it's in their nature to destroy their prey, so they dig out the "innards" of the toy. i have also seen some toys that sort of "hide and stuff" smaller toys on thatpetplace.com
http://www.thatpetplace.com/Products.../Itemdy00.aspx
(the place that sells the marmot) and they might be good.
but no matter what you buy you have to be careful once they pull that stuff apart!
kongs have lasted longest for me

good luck!