Being a relative newbie here, I still remember clicking to accept this and accept that, and I'm sure that one of the things pointed out to me was that postings are the personal views and advice of the people who posted them. So in essence, anyone posting here has already accepted that. I don't see a need for a statement....
MM, paid or not what you do in your own time is your own affair, and as long as you don't post anything potentially spurious toward your employer, your employer cannot stop you.
Tell 'em to shove off!!
Better still, do a flounce of the highest order, photostat your 'personal bits' and fax it to your boss along with a copy of your solictor's letter to the Court filing for constructive dismissal.