Hi All,
I hope some of you find this useful.
The achievement "Raiding with Leashes" Raiding with Leashes - Achievement - World of Warcraft, does not actually require you to own or buy any of the pets. You can simply "borrow" the pets required from other players/friends, use them, and then re-cage them and give them back and it still counts towards the achievement.
On the flipside, if you have all the pets, you can sell the achievement to other players who want the 10 points and/or "Mr.Bigglesworth" Mr. Bigglesworth - Item - World of Warcraft (which is a reward for completing the achievement and famous for his "Naxxramas Shenanigans"). Simply find a buyer, cage the pets, trade them over 1 by 1 and then have him re-cage them and trade them back.
Thanks all and see you in game
JP