Somewhere in PT I answered this but I can't remember where...there are so many categories I forget what I do where.

At any rate, I was advised to tack up furring strips (available from Lowe's, Home Depot, etc)
OVER the basebards. A furring strip is usually made from an inexpensive piece of pine and comes 1- 1/2 inches wide and up to 6 ft long. Then you just nail it over the baseboard. It looks a little tacky to us but the buns end up chewing on the furring strip instead of the bb.

Then when/if they work themselves out of that destructive habit, you can remove the furring strip and you have your baseboard back...... This is esp important for those of us who rent!!!!
After I felt I could take the furring strip down I filled in the nail holes and colored in the teeth marks and the damaged part of the bb disappeared (except upon close inspection).

I've noticed that when my guys are bored is when they get destructive so I try and keep them occupied with toys, food and each other. I just bought them a wicker tunnel from Busybunny.com and they LOVE chewing on that. The trick I've found with the toys is that the toys need to be rotated so the buns don't get bored with them.
Hope this helps.