What's the best substrate?

[Ruby]

I would say that "spot cleaning" only goes so far, as germs are left that you cannot see- & it becomes a health issue- not just about the odor.

Oh of course! No matter what substrate I'm going to change it out every month and spot clean weekly.
When I said "Last a while" I meant something I could buy in bulk? Just something that comes with a lot of substrate.