I live in southern British Columbia.

http://i.imgur.com/bLgCn.jpg

They grow in clumps, mostly along my neighbor's fence (neighbor doesn't bother to remove them). I am getting tired of them coming back all the time. I cut the ones on my side of the fence to the ground, then sprayed the stumps with Roundup. It's been a week and the stumps are growing new leaves again. Some of the plants I sprayed but didn't cut down had some leaves fall off, but otherwise seemed healthy. Everything else along the fence is nice and dead, but not whatever these things are.

I searched the BC government's invasive species database, and couldn't find a match. I've seen these plants before, and have always heard them called a weed, but nobody seems to know the actual name. Would like to know the name and a way to stop them coming back.