"These ancient sites have always been under threat by ignorant people and it is only by spreading our extensive knowledge can we educate those who would wish to harm them."

Most people are ignorant in the true sense though, they just don't realise. You can go on Avebury's banks and on top of long barrows and (by tradition) your kids can slide on the prostrate sarsen at the Eastern entrance, but you mustn't climb other stones, or on Silbury.
More and better signs are the first step I'd have thought.