A possibility
Taking a cue from the manner in which tubeless tires are "patched", I think if you could devise some "plug" to put into the tear, the same way that a plug is placed into a tubeless tire, you just might create a viable repair.Thus, you might take the fender to a garage or tire place and see if they could possibly make a repair for you the same way as for a tubeless automobile tire. It will probably be black and may not look very pretty, but certainly possibly less expensive than a new 10 X 30 fender. Perhaps some white electrical vinyl tape over the black plug may hide the repair or at least prevent it from marking either your vessel or someone else's.