This is a good question, my mast goes up to about out 31ft, it is attached to my roof and is about half a meter highter than everything else including the near by houses and their chimneys, this is because i wanted good reliable readings. Anyway, i have not yet earthed it, but i should as it is likely to get hit, being on an aluminium 7ft pole, and being higher than all the other houses. But to earth it all you need to do is attach some copper wire and make a spike that is higher than your pole, so the lightning strikes that first. Then route is safely to earth, basically wire it up to the ground, making sure it satys well away from anything that could get damaged, and you should be O.K then.