Illegal to be within 3m of the fence?

[Erik H. Bakke]

I was approached by the AFP while taking some photos at the 25 fence this morning.
They claimed it was an offence to be within 3m of the fence, so I could stay at the other side of the road, but the grassy strip next to the fence was off limits.

They were quite friendly about it, and I wasn't going to make any protests about it but this was quite a surprise to me.
I thought that anywhere outside the fence, unless otherwise restricted, was OK, and that the 3m limit really applied to using ladders.

Any comments?