I've got two bulldogs, and believe me we've gone through everything. The few toys we've landed on that seem to have some durability are the hardened plastic frisbees at petco, the mini tires they have do pretty well, and then we always get them the giant knotted ropes, those last for a while.

http://www.youtube.com/user/hp330v8?.../9/7agV6P9SHyA