Quote: I have seen very small ones for sale in my area, only suitable for young chicks or other baby fowl. I think regular ones are too big and cumbersome to keep at a store. You may be able to buy some online, I think, but they are probably on the expensive side. It is definitely possible to build one, though I've never done it. Look around online. Try searching "DIY chicken tractor" or maybe "how to build a chicken tractor". It should be heavy enough that the birds can't scoot under it, but light enough that you can move it every day.
Here's a link that might help. It's designed to hold many broiler chickens, so the size won't be right, but it'll give you an idea of materials needed.
http://www.grit.com/departments/how-to-build-a-chicken-tractor-zm0z12ndzgou.aspx?PageId=1
If that link doesn't work (not sure if I did it right,) just search for "GRIT magazine chicken tractor" and click on the article from grit.com.
PS- In answer to the original question about tearing up grass, it depends on the breed. African or Chinese geese (Descended from the "swan goose" species) are more likely to rip up grass from the earth. Other geese (Descended from the greylag goose) don't do that. My geese were purchased as "American" but they have small knobs on the bills and their coloring is slightly off, so I suspect some African blood in there. They do rip up the grass some, but not too bad.
Also, sorry about your duck. If you have crows in your area, throw out some food scraps to them. They chase hawks away, and just their presence alone seems to intimidate them. I give them old fruit and any eggs that the ducks managed to crack. (Just make sure the crows eat it and not raccoons, possums, etc). Also don't do this if you're planning on ducklings or goslings, as I've heard crows will go after them.
Hope all this helped.