Hi Yam,

I'm not sure how big your plots are but at my community garden we had 20x20 square plots. Each corner was marked with a metal T-stake and we wrapped around one of the "front" stakes,metal wire. Attached to the metal wire was an aluminum plate (probably half an inch tall by 2 inches wide). The plot number was then etched into the metal plate. It seemed to work just fine. Hope that this helps.

Josh

IN OUR COMMUNITY GARDEN, THE PLOTS (20' x 20') ARE ARRANGED IN SQUARES,(4 PLOTS TO A SQUARE), WITH 36" WALKWAYS BETWEEN EACH SQUARE. EVERY TWO SQUARES, ON ONE CORNER, IS A WATERING OUTLET.
IN THE SPRING, AFTER SIGNUP, A MAP OF THE PLOTS, W/ GROWERS' NAMES, IS MAILED TO EACH GARDENER. THE GARDENERS ARE ENCOURAGED TO STAKE & STRING THEIR PLOTS TO GET STARTED, & THE STRINGS ARE LATER REMOVED FOR EASE OF WORKING & HARVESTING...
PS -- ABOUT 1/3 OF THE PLOTS HAVE SOMETHING GROWING YEAR-ROUND, SO IT IS EASY TO SEE THE GARDEN'S OUTLINES...
GOOD GROWING TO YOU, K.

You know what might make good markers? Ceramic. Find someone who's a potter, or even ask a school art dept. for help. These could be rectangular, about the size of the address numbers on a house. You could place them at the same corner of each plot.