When all the bark is gone from the top of the hanging sticks, I turn it over and then they can chew it the rest of the way, lol. Reversible toys! Last twice as long!
When it's completely debarked, I replace them. Each cage has at least 2 hanging toys, and I made little wooden toy boxes for them, and every night I throw in some twigs, willow, pine blocks, etc. in there so they can dig and choose.