STI doesn't have the strongest of finishes that I have had or seen. Safariland has a swead (sp?) lined holster. Problem is, unless you have a sheepskin lined holster, all of them are going to cause wear of some sort.
If you are looking to refinish the gun at some point, there are some very hard/durable finishes out there. Hard Hat treatment is one, Ion Bond another. IF you are looking to compete, you are going to get wear no matter what.