RE: how often
The two tarsal gland scents that I am familiar with are ' Charge II' by Buck Stop and ' Tarsal Gland' by Code Blue. I think Tink' s makes one, too, but I don' t know the name. I' m not sure if you can find them at a Wal-Mart, but I' ve seen them at the bigger outdoor stores like Bass Pro Shop Outdoor World.
My father-in-law and hunting buddy uses the Charge II and has lots of venison in the freezer and racks on the wall. Last year I used Code Blue' s Tarsal Gland, and it helped me bag two bucks and two does.