I have some shrubs I need to kill that are along a lake shore. I
cannot use any chemicals--natural or otherwise. I also won't be able
to pull the shrubs out. Their roots are too strong and the terrain
would make it impractical. If I cut them back, they just sprout right
back up.

Are there any ways I can encourage these shrubs to die? Perhaps by
cutting them back a different way? Scraping some bark off? Covering
them up? I'd be interested in hearing any techniques you think may
work.