If you plan to work him I would stop using squeaky toys for retrieving, this can encourage some dogs to mouth/bite down on retrieves which is obviously not good when they're retrieving game. It's generally best to try to avoid creating potential issues like this.
To get him bringing in retrieves start in a confined and relatively boring area, don't practise in a big open field where there's lots of room for him to run around and things to distract him. If he's running past you put your back against a wall/fence/hedge etc. or stand with your back into a corner so he can't run past. If he's just running around put him in a channel - make one in your garden, use an alleyway or even the hallway of your house. Throw short distances to begin with and get down to his level to encourage him back to you. If he does come back don't be too keen to take the retrieve off him, let him hold it for a while and give lots of praise. If he's messing around and not coming back stand up and walk away, don't keep calling him or turn it into a game. Encourage him to follow you - if you're doing it in the right kind of space there won't be anywhere more interesting for him to go - and again don't take the retrieve from him too quickly, let him walk alongside you and then gently ask for the retrieve while giving lots of praise. Don't pick up anything he has dropped on the ground, if he drops the retrieve encourage him to pick it up again and put it in your hand while again giving lots of praise.
