Which training for this 2 year old disobedient dog?

[BoysBoysBoysAndMe]

My mum got a cairn cross shitzu about a year ago off a friend of a friend of a friend iykwim. He's never had any proper training, not very socialised. Mum took him as owners didn't want him any more and it's my mums first dog.

They absolutely dote on each other. Mum panders to his every need. Cooking him fesh food every day. Taking him for a couple of walks a day. He even sleeps on her bed! - she's single!

Anyway, dog is completely disobedient and runs the house an mum let's him get away with it. But she finds it frustrating that she can't let him off a lead, because he won't come back-at all. Hes quite protective over her too if they're out and he regularly growls at passers by and sometimes even tries to nip their trouser leg!

What's the best way to get this dog trained? Any specific book? Training methods? Can you really teach an old dog new tricks?

Mum goes on lots of walks in woods, national trusts, trans Pennines walks etc and although she takes him on his lead, try would both live for him not to be on one. Any advice would be great. Thanks

[BoysBoysBoysAndMe]

Just read the doting paragraph and doesn't sound very doting-just normal care... But they do dote on each other

[JaxTellerIsMyFriend]

She needs to get the dog and her enrolled in a local training class. Socialisation with other dogs and people in a controlled environment will help a huge amount.

Long line for recall issues and lots of praise and treats when he does return to her.