I used this on my lads cage corners and it works a treat.
its a nail treatment for adults and kids like in a nail varnish bottle and it contains bittrext which tastes VILE!!!!!
i can only compair it to hairspray / laquer, concentrated grapefruit pith and vinegar [yeah i tasted it, urghhh!]
if your wanting it to stop ratty biting his/her cage then just paint it on, let it dry and ratty soon learns that biting that corner/object tastes gross and leave it alone and you can stop using it after a while.
took my lad about 3 weeks to learn that gnawing at that is yuk!