Im not an expert but we have done something very similar to what you describe, and he is always good when there is a lead attached and in enclosed areas and will come back every time. We just cant seem to master it off the lead. I do the whole reward and make a big fuss when he comes back, roll on the ground and play... i try and be exciting but at the moment i just cant seem to compete when his attention is somewhere else - but then there lies the problem - he should be attending to me right???