It might be worth getting something like a fingbox to plug into your router, then you can control access by all devices (whatever he has now and in the future) and it will also work with any other router/isp you switch to without any changes - you can also get a warning if/when he unplugs it via an app on your phone.
They cost a bit, but keep your eye on the price as it varies a lot (typically £65-£100 but they keep having various offers).
They cost a bit, but keep your eye on the price as it varies a lot (typically £65-£100 but they keep having various offers).