Goldfish-proof moss

[maryavatar]

I have a large cold-water planted tank, and foolishly volunteered to look after my grandfather's fan tailed goldfish when he went into a nursing home (and yes, I know goldfish are horrible fish for tanks, but the only other option was flushing it). Most of the plants in there are hardy grassy plants which the fish ignore, but the goldfish completely destroyed all my marimo moss balls.

Can anyone advise on moss? I'd planned on getting some java moss, but not if it's going to be chewed up.