hey,I use a a bit of carbon fibre on my down tube,very hard to get hold off,but does fab job.
Or you could use an Armourdillo,i have two don't ask why.
But here is something that is better than all,and is cheap,if you go to a boat yard shop,they sell loads of this piping they use on the boats,just cut it throw,guite thick stuff,no chance in hell of dents or anything.cherrs jake.