Use white spirits from Bunnings to get the glue off next time - I put kitchen role on the board and pour the spirity over that - leave it 10 mins and it comes off like thick glue using an old kitchen plastic spatula - real easy and no sanding !!

may need to do this about twice. To finish just rub with a wet towel with white spirits then wash with soapy water
To get the old deck grip off I leave the board in the sun for half an hour to warm it up ----- then peels off easy......
I've done about four deck drips with this technique and no damage to the board