Alexander plants/weeds

hi guys, anyone have any ideas of how to control/remove Alexander’s (Smyrnium olusatrum) from a garden? The grow out of every orifice going Andy trying to dig down and remove the taproot is damn near impossible for Alexander’s next to other plants I want to keep, underneath ornamentals rocks and between paving slabs! 

Im keen to try and come up with some solution before they flower in spring and summer and make things even harder for me!

any help would be greatly appreciated