I would think that anything that covers your scent, and anything that would be common for a moose to smell, would be ok. If you are just using it as a cover, and not as an attractant, then you can use the urine of any animal that the moose would not take offense to that is common to the woods that you hunt. Fresh is always best, but I'm not really sure how you would collect fresh cow moose urine, besides killing one? Maybe a ghillie suit and a tin cup on a cane pole?