I rotate toys every few days. I have accumulated a ton, so it helps with clean up (less to pick up each day-though they still always have a basket full) and keeps the toys more interesting since just when they start to get tired of the toys, I bring out "new" ones.
Leroy does have several favorites (stuffed alphabet blocks) that I leave out much longer. He has 5 or 6 since they were only $1 each and doesn't really seem to favor one over the others. So I leave half out until they need washed, at which point I give him the fresh blocks and clean the dirty ones, putting them aside for later.
Other favorites such as kongs and cowhooves are only down when I am watching, otherwise I end up with someone (aka Penny) stealing toys from the other dogs and taking them to her bed to RG. She doesn't chew, only sits with them around her while giving the other dogs the "look".