Older Dog Marking Inside.. What To Do?

Hi all.. my 8 year old cockapoo started marking inside the house about a year ago. I don’t know why he started so late, but it happened about 6 months after my mom moved into this house. I’m back at home and can work with him if it’s possible to train him, but he was never neutered. I’m wondering:
A) Is it possible to correct this problem with training?
B) What risks are there for an older dog to get fixed?
C) Are there any things I should be sure to ask a vet if we do have to go this route?
He’s still as chipper as can be and crazy energetic, but the thought of him going under with anaesthesia scares the heck out of me. Let me know your thoughts, thanks!

Our 14 Month Old Cockapoo Has Been Trained To Potty Outside But Sometimes She Forgets And Goes Inside.?

Is someone always there to let her out when she has to go?