I have been having the same problem, my 7 month Newfoundland has managed to destroy most of her toys, sometimes i used to freeze a rag soaked in water and tied into knots and this was very cooling on her gums while teething.
Have a look at this on EBAY as i have bought one, its supposed to be fairly undestructable

Tug a Jug interactive treat and training toy Med/Large (#270285903293)

Will let you know what like when it arrives