Silbury Hill 180
Image by photobabe

No doubt in my mind that increased access would result in increased damage.

Repairs would never keep up with demand.

How about a wooden staircase being errected up the hill with a viewing platform on top?
I know this would cause damage where the supports are inserted but at least there would be no excuse to walk on the 'hill' itself.
Obviously this only applies to those who ignore the signs not to walk on the 'hill' in the first place!