for the last 2 months or so he has been consistently jumping 18" crossrails
I'm a big fan of "not beating a dead horse" with one thing. Just how "consistently" have you been doing this?
Its nice to jump... but if he's got the point and he clearly jumps these 18" crossrails nicely... Hasn't he EARNED the right to a trail ride? A trot around some poles? Some different patterns and activities in a different arena or on a trail or driveway or filed?
So... what does HE want to do? Have you asked that at all?
Lets put it this way, I train barrel horses. Most people run there barrel horses in the pattern every time they ride. I run them once ever 10 days for a few times around and if they're still sharp we hit the trail, we do some flexing in a field, we hop over a few low jumps or trot ground poles, we do something different with every ride.