Terry Pinnell wrote:
I'm fighting an ongoing battle against weeds growing through the
sand-gaps in out brick paths and patio. I spent the weekend clearing
them, this time with a high pressure hose, and refilling with fine
sand. So now I want to do whatever I can to PREVENT their
reappearance. Or at least postpone it for a long time.

Brush in a little sodium chlorate weedkiller.