Plants I've found that can stand against goldfish attacks are swords, java fern, dwarf sag, vallisneria (to an extent) and rotala. My goldfish ate/killed anacharis, hornwort, cabomba, and anubias (by ripping off the roots). You can check out my journal in the link below for more details on how I set up my goldfish planted tank. This guy also has a great goldfish planted tank http://www.plantedtank.net/forums/t...935-46-bowfront-goldfish-grazing-project.html.
Swords and crypts seem to do well with my gold fish. Java moss also does fine although they may tear pieces off which then drift around. Pretty much any plant with thick tough leaves will be fine.
If you want something healthy for your gold fish consider growing duckweed for them. It's a good source of plant matter for them. They will devour it completely so make sure to have a separate tank to keep a supply growing.
My biggest piece of advice is get small goldfish; the younger they are when they get used to plants the less likely they will eat them when they're older. Also, sometimes you just have to get lucky with the temperament of each fish. Making sure that they get enough plant matter can help too; mine's diet is about half algae wafers.
My goldfish doesn't really eat a lot of my plants, just pulls them up until they have good roots, or knocks them out of the ground by nosing around the substrate (I have a comet).
Plants he eats are: duckweed, frogbit (pretty much any floaters get eaten or shredded), and he trims the java moss so that it stays close to the log (which I actually like). As a previous poster mentioned, I use him to git rid of extra floating plants from my shrimp tank.
Don't count on any carpet plant unless you can get it established first; goldfish are just too curious and will pull it out, causing you to pull your hair out. You might try a bigger carpet like dwarf sag which tends to have a larger root system to plant, but be prepared to keep reinserting floaters.
Plants that he doesn't eat in my low tech set up are crypts, several shapes of java ferns (narrow leaf ones do fine too), pennywort, Hygrophila polysperma, H. difformis, golden creeping jenny, swords, and hornwort. I've heard people say that they eat hornwort, but he totally ignores it.
Plants I haven't tried but have heard will work are crinum sp. and various lotuses.
You've tried swords and they won't stay planted? How deep is your substrate? It really needs to be at least two inches deep to give plants room for their roots, and will also give you enough depth to bury it well. Planted tanks usually have 2-3 inches of substrate. Also, some people suggest stacking small stones around the base of the plant to keep diggers away; that might help keep it down until it can grow some roots and stay down by itself. Adequate lighting and nutrients also help a plant grow faster and stronger and stay down on its own.
Yes they do, but they tend to be really expensive. I would look online at Amazon or a place like that, or (better yet) search on the swap and shop on this forum; there are a couple people who sell them.