I need to toilet train my 3 yr old alaskan malamute!!!!?

We've just recently bought a 3 yr old alaskan malamute. He stayed outdoors with the previous owners & has never been toilet trained. When we first brought him home let him come inside but he lifted his leg on everything including my mum in her wheelchair!!!!!! We would dearly love to let him inside as we already have shih tzu who stays in most of the time. It makes me feel so guilty leaving him out in the cold all the time. Any tips or suggestions would be greatly appreciated