there are a lot of sturdy fabrics out there.
this is a German site with English text. I do not think, ordering from Germany would be necessary. But there must be US-Companies around. Maybe just get the idea from the linked page.
There are interesting and sturdy nylons out there, also other tech-fibers. And then there is heavy cotton. If you want to do the overkill-version (and weight does not matter the most of all) try getting some sail material for sailboats. that stuff will withstand a LOT. Since it will not have to be waterproof you can just sew it up.
Knitting would not be my option for this purpose!