But, no go.  Two of the five basic philosophies of NATRC are :
(1)To stimulate greater interest in the breeding and use of good horses 
possessed of stamina and hardiness and qualified to make good mounts 
for trail use.
(2) To demonstrate the value of type and soundness in the proper 
selection of horses for competitive riding.
To allow a horse who interferes to wear boots for protection would go 
against these philosophies.  They did not even want to santion a ride 
that would allow such a horse to compete, fearing it would imply that 
they were condoning the selection and use of a horse inappropriate for 
trail riding.  If you want a better explanation, e-mail me, and I'll 
give you the name and number of a NATRC Board Member who would be happy 
to explain it further.
BTW, if your horse is interferring, have your farrier check the lateral 
balance of the hooves.  My horse interferred (had to wear ankle boots) 
until my farrier did some serious measuring "stuff", and I believe my 
horse was long on the inside.  The farrier made an adjustment, and the 
horse has been fine since (4 years ago).
You might want to try endurance - limited distance.
Hope this helps.
Kathy
Border Creek Farm
bordrcrk@ix.netcom.com