I have heard there's a better chance of success when you try to enchant things when you have full troops and spies. Dunno if its a fact, but otherwise yeah sometimes the mage likes to fail over and over. I got too caught up with enchanting something and it went from lvl 7 to 2 a couple times.
I've also heard to do it when your troops are full so really who knows when it's best to enchant. You kind of got to just hope for the best and keep trying.