i never use a single skin or tennis ball or whatever i want the mutt to retrieve use 2 , that way the possessive element of its instinct wont kick in, he wants the skin and the grub,and thats the way the pups nature is,
,,throw 1 as soon as he lifts it get him excited bout the other one, that way hopefully he'll run up to you with the other item in his mouth, tease him for a few seconds with the second one
, he will drop the first one
, then throw the second , repeat this over weeks a little at a time, until you become the focus of attention not the skin ,,you will end up with a fast ret