Go to shadowmoon vally and find the pitlord named Azaloth
Azaloth - NPC - World of Warcraft
He is immune to all damage but you can still train skill on him without aggroing any mobs (lvl 80)
Dont flame me this is a repost i have just seen so many ppl posting about hitting guards and hope that you miss and get skill. So I think this is the best way.