I converted my existing greenhouse to a duckhouse using the existing shadecloth sides, just adding chicken wire where necessary. However, I currently find mice eating holes through the shadecloth. ‘Petrified hessian’ might be the answer.

I did a little research, and it is basically a cement mix covering the hessian. Other materials can be used, including old sheets in place of the hessian. The hardest part is apparently getting the cement mixture onto the material and the material fixed in place before it dries. However, I would think you should be able to do this without too much trouble at all. I cemented the surround to my duck pond all by myself (and I’m a little old lady) the secret was to mix a small quantity and apply it quickly. Choose a cooler day and the mixture won’t dry out as fast.

Here is recipe for petrified hessian from Yahoo Groups

5 liters water
5.5kg cement
900g lime
450g salt
225g alum

(Source: http://groups.yahoo.com/group/papercreters/message/10277)

Here are a couple of links to petrified hessian buildings:
Earthbag building
Burlap-crete

Good luck. Let us know how it goes if you try it out.