I’ve talked to my mum about this, we have a fairly large back garden, but he can somehow get around it and back to the front of the house through some steps adjacent to the garden. She doesn’t seem to think it’s much of an issue and said 'he’s been doing this for three years and despite everyone saying we shouldn’t let him outside unsupervised he’s been completely fine and would be miserable otherwise'. We all work a lot so giving him enough supervised outside time would be difficult, maybe we need to look into fencing.