Can a landlord charge you late fees for past months that were never charged when rent was paid late?

My landlord's wife got mad at me because I would not climb on the roof and put a tarp (that I would have to pay for) over a new leak. She began to threaten to go back and charge late fees in past months for rent paid late. Now I do pay rent late every month, but this is often because I am nervous about paying and can make repairs that I make out of the rent. I do pay it late (however, it is paid every month), but often they will go days to months without doing the repairs (9 mo to fix a leaky tub, 1 week no hot water, 2 weeks no heat, etc). Only after I get mad and go off do they fix things. I have pet potbelly pigs that I am not zoned for but they agreed to them, so its not like I can call code enforcement. I have only a few months before I can move, but am in a bind for now