Symphoricarpos (waxberry) being a nuisance

I have some of these shrubs that started in a corner of the back hedge when we bought the house. Having had no experience with gardening before that I didn't realise what a jerk this plant would grow up to be so I didn't get rid of it when I had the chance. It's now spread all along the back of the fence where I can't really reach it and it's spreading along by the neighbour's fence as well. It also pops up between the patio slabs. To complicate matters there is an empty field on a fairly steep slope behind us, which is owned by the council but I've been unable to find out how I can get access to it.

I've sprayed bits of it with SBK but it's hard to reach all of it without spraying the plants I actually want to keep. I've thought about trying to climb over the fence and renting or buying a strimmer to try and cut it all down, then spraying the stems with SBK but I don't know if that will actually work to keep it under control. Or just cutting as many as I can reach and painting the stems. Any suggestions?