A big weeing/marking problem

[ChihuahuaMummy1]

I have a 3 year Chihuahua,he was an angel from being a puppy; slept through straight away,weed outside etc.
Ever since hes reached maturity over the last year hes marking in the house and it stinks.I clean it up straight away with the enzyme cleaner but hes still doing it in the same spots
1.On shoes (we keep them higher up now)
2.against my sons toybox
3.against the TV cabinet
4.Anywhere upstairs if he gets a chance

If I got him castrated would it help? I've heard this works only if you get it done very early.Please help!

You should have had him neutered for a start at least

What has changed in your house in the last 3 years

^except for maturity
Have you had another baby
Is your baby now walking

Etc etc

In hindsight yes maybe we should have got him done earlier.Absolutley nothing has changed apart from the fact hes now an adult male