Would like to add live plants

I would like to add live plants to my freshwater 55 gal aquarium. I have
tried some in the past but the fish eat the plants faster than they grow
and after a week or so nothing remains. I have 4 large silver dollars
which seem to eat up the live plants the fastest. Is there anything I
can do to prevent this or should I stick to plastic? I have only tried 2
or 3 plants at a time. I thought it I put in a lot of plants they would
have a better chance of growing faster than the fish can eat them. Any
ideas?

Andy Arhelger