Thank you so much! I will mention this to my farrier and see what he says. I have heard a little bit about locking stifles, but none of the signs I remember reading have been shown by him. Besides that one trail location he has no slipping problems, and while working in the round pen I have not noticed any abnormalities in his gait. However, I will also mention this issue to my farrier and see if he believes that to be a possibility as well. If so, I'll get a vet out ASAP.
Also, yes, I thought that might be the case with the conformation. I will try and get some better pictures of him tomorrow morning.