Thanks everyone. Yes, I considered a prehardening bath for the reasons described here -- it would potentially protect the film from the beginning. I didn't want to add the complexity, though, if better tempered baths and a hardening fixer would solve my problem. I'll reconsider it though. I found a source for chrome alum, but I have no experience preparing chemicals from scratch like this.
I also considered Pyro, but I didn't want to start from scratch with a new developer (my repertory is already pretty broad!). I was also a bit put off by the statements about how the tanning/staining affects printing with filters. Right now I'm using XTOL and I like the results I get.
My current rinse method is a variation of Ilford's: Instead of 5+10+20, I'm using 1+1+5+5+10+10+15+15+20+20. Maybe that's excessive, but I wouldn't expect it to cause problems. Even so, I don't think it's thorough enough to rinse after a hardening fixer.