[nagdu] toy suggestions?

[Julie J.]

Does anyone have any good recommendations for toys for EXTREMELY hard chewers?  I especially like the ones that require extra thought, problem solving or are unusual.  That's not absolutely essential though.  I'd also like it if they were large enough so that they don't get shoved under the couch.  *smile*

We have the usual Kong, rope tug, large rubber ball, a large spiky thing that Orca makes and a Nyla bone.  Stuffed toys are totally out of the question.  He very much likes tennis balls or the variety of tennis ball type toys, but they don't last long.  

TIA
Julie