Found this site for copper tape, a lot cheaper than the marketed slug tape at anywhere from £5-£9 for 4m, I would say that the 1" roll at 33m meters would be the best as the 1/2" may not be wide enough. £26 for the roll. Will be getting some myself when I get home for my raised bed and stapling it on.
Kemtron UK - Online shopping - Conductive Foil Tapes