Dog gone in a sett?
Dogs, especially terriers, love to investigate holes. Too often they disappear down them and the owner panics. Sometimes the dogs return very quickly. Sometimes it's hours, even days before they re-emerge, as most do eventually. Don't take the risk. If yours is a dog that likes investigating holes, as many terrier types do, keep them away from holes (or securely restrained on leads while you pass by) unless you are sure the holes aren't entrances to a badger sett.
Badgers are powerful animals and defend their homes fiercely. Dogs that enter a sett can suffer very severe bite wounds. Better to be safe than to be sorry. So keep your dog away from large holes, especially those with a lot of spoil at the entrance. Huge mounds of excavated soil are inevitably a sign that it's a sett and that badgers have been tunnelling, creating what should be a secure home for themselves. That's the last place you want your dog exploring.
Digging is NOT allowed
It's an offence to dig into a sett (even if a dog has disappeared down one) without a licence to do so from Natural England. Even fire brigades are not entitled to attempt a rescue dig unless they have a licence authorising them to do so, or can show it is an emergency and a dog down a sett is not normally an emergency. Usually the fire service personnel are required to wait for at least 48 hours before digging into a sett, and they are not always able or prepared to undertake such an assignment.
Keep dogs, especially small ones, away from badger setts! Remember, badger baiters put dogs down setts so that they can locate and then capture badgers, which are then cruelly treated or killed. That's one reason why badger setts are protected by law.