How often should I seal my rubber mats?

Two thin coats of sealant applied to clean and dry mats for sealing.  Once sealed the mats will wear based upon usage so it is difficult to say often they need to be sealed.  After sealing mats should be protected from dragging gym equipment across it and other harsh usage.  Most dog day care and training centers clean and reseal with at least one coat of sealant every year.  Some have gone much longer than that.