I helped build this lock-down device for Greenpeace. Its a bus converted to look like a tissue box, and two 55gal drums inside filled with concrete and a steel pipe inserted into it. The Activists stick their arms into the pipe and lock themselves in. I cut holes in the side of the bus so the activists could be seen and still be locked in. I think they slashed the tires, so the only way to move the bus was to jackhammer the activists out – a time consuming process.
You can read all about the greenpeace action here.