It was pointed out to me on my server that EXP Gems were although a cool way of earning EXP in minecraft.. but at the same time it rendered the Mending Enchantment useless as my plugin cancelled EXP Orb drops upon mob death.
Mending works by flicking a random interger when you aquire a new orb and the game decides if that number will be accepted to activate mending on your item.
EXP Gems will now throw 1 orb at the player when a mob dies so Mending now works as expected.