first off, yes they would be VERY effective in clearing these plants. as far as the fencing, they would get out very easily. they find ways. I have field fencing, with barbed wire across the top and the bottom is tent staked to the ground in between the fence stakes. I still have two main goats that find ways out. get something to fill in the gaps between the bars.

Thanks. That's great news, about the plants! Do you mean that they would get out even with the electricity on? Would just wires in between the bars work or do you mean some sort of mesh-like thing? What is field fencing, by the way?

field fencinng, is about 2x4" at the bottom and 6x6" openings at the top, or you can get regular 2x4" opening fencing all the way around, I prefer it to the field fencing. A friend of mine, had electric fencing hook up and the goats would try it, over and over again, until they figured a spot that was spaced just right, or when a branch would lean up against it and stop current, they would get out. It didn't stop them very much.