Wood Protection

We picked up a second hand bigger hutch last night, and its a similar cheap wood to the one we are replacing but want it to last a little longer.
I treated the old one with some wood stain for the weather but then they still chewed every bit possible. What can I use on this one to try and prevent the chewing? Some said the same stuff they use for horse stables but buns are a little different to horses!
The stop chew spray from pets at home may aswell have been water for the use that did! Does anyone have any ideas or tricks?

You could use metal plasterboard corner protectors similar to this http://www.wickes.co.uk/Wickes-Thin-Coat-Anglebead-2-4m/p/240322
Do they have plenty of space including an attached run? Unlimited hay? I would give them plenty of things to do and things like apple tree branches to chew

Yeah I looked at them but got warned they are sharp so looking into something else. No the run is on the grass I pick them up and put them in on dry days otherwise they have hay in a hanging basket thing, some shop bought twigs all tied together, and some almost kindling wood tied together and two other toys minimum in the hutch.