Question
what types of plants should we put on the abnk of our pond to stop the erosion?

Answer
Clare,

The simplest way is to just sod the banks with a good quality grass sod.  Whatever variety that is suitable for your area is fine.  Grass can also be planted by seed.  

I need to know where you are located to recommend any type of ground cover.  Different varieties are recommended for different areas of the country.

Thanks,

John