How to reduce urine smell?

I have two 4 month old females in a double critter nation.



After about 2 days their cage smells like urine just when I walk by. It is currently fleece lined and I have a litter box with newspaper pellets I think. I know they don't use the litterbox religiously but they do pee in it sometimes.



I have ordered bass pans for the cage. Would switching to pine shavings cut down the smell?



I was hoping to just clean the cage once a week, vs every two days. Is it normal for the fleece to smell this fast?



Thanks!