I've been doing some rehab work for a recent knee injury, and they have turned me onto the whole foam roller thing. Now I'm not against spending the money to get new rollers, but I have noticed that they break down after a while and don't work as well anymore. I was looking for a substitute earlier today, and my nalgene bottle is just about the right size, and its much more durable than the rollers. Assuming I can tolerate it, would it be a good idea to use something harder than the foam to roll out my hamstrings, IT band, and soleus?