I'm going through this course with two of my dogs. 

Sisko, my 7 yr. old Labrador Retriever,  is a lower drive dog who has never shown a lot of toy drive.  He is very food-motivated and has been easy to train that way.  I didn't attempt to play tug with him until he was already an adult, partly because he was so easy to train with food so there didn't seem to be much need to play tug and partly because his breeder is dead-set against playing tug because she feels it will result in a hard bite.  That's not something you'd want in a hunting dog.  (Sisko is a pet dog, not a working retriever.)

Sisko will now play tug although he's still a bit tentative in his play.  I'm finding that at this point I need to make it a bit easier for him to "catch" the tug because he tends to give up if I make it too difficult for him.  He's also not bringing it back to me -yet- when he "wins", but will bring it back if I apply light leash pressure.   So, we are making progress--slowly.

My other dog, Toby, is also a Lab and is two years old.  He loves to play tug (and is somewhat less food-motivated), but doesn't always play by the rules.  In the house, he is now bringing back the toy at least partway, usually within a couple of feet, so I "reel" him in the rest of the way.  Outside, I'm pretty sure he would take off like a shot with his "prize"  and try to engage me in a game of "keep away".  So, we will definitely be using a leash or long line outside.  We haven't gone outside yet because it has been so cold lately, but once the temperatures are above the single digits we'll take it outside and see how it goes.