on the plant shelves? how deep is the pond? you could elevate the planters on blocks if you like. i personally dont like plant shelves as they take up too much swimming room for my big koi.
another option would be to just dig out an additional plant border if you have room. but then again you already ordered your liner and that prob wont work...
another option would be to just dig out an additional plant border if you have room. but then again you already ordered your liner and that prob wont work...