Possive with toys and my other dog

Question
I just got a 5 month old male Heeler/Australian Shepherd mix from a rescue.(Oscar) My other dog is pure breed female Vizsla 3yrs old. (Lexie) They play great together, eat together he is not aggressive about old toys but is seems when there is a new toy introduced, and we buy two of the same, Oscar at some point will decide that it is "his" and attack Lexie. Of course we intervene and end up getting the worst of it. Lexie won't back down either.

Answer
This is true possessiveness, quick, short snaps, hackles raised, stiff legged, and not just ''Its more fun to fight over a toy with another dog''?

If so, you must start with stronger leadership.  The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat.

Once the dog is obedience trained and sees you as leader, you should be able to have it sit and then release the toy to your hand at the command ''Give!''.