It sounds to me like he is napping for his mates......keep up the work with insisting he goes out on his own but make sure he gets to go out with mates too! I would only use the turn as a means to an end eg...to turn back the way you were going. Make your outings alone short for a start and then build them up to longer and further away from home. Does he act up when he can still see and hear his mates? Have you taken him out of earshot and eyesight of them? When we first got Chinita she would do this and it would drive me insane!!
so I started tacking her up and walking half a mile down the road before getting on and having a ride...yea at the start she would pack a wobbly...screaming out and trying to go back but I used pressure release and slowly she came with me...once away from everyone she was good. Just an idea anyways. :)