I was thinking about the glue going through the screening, too, Sharon. The answer is we need to have the screen suspended in a frame, glue the pennies to it while it's suspended, then cut the screening after the glue is dry. A modest dot of glue for each penny, hopefully not too much would drip, but a sheet of newspaper underneath to catch the drops . . . might work.
Thanks, Natalie. I'll try pulling the mulch away if I can't make enough slug necklaces . . . my daughter's yard at the previous house seemed to have 'way more than its share of snails. We blamed the neighbor, who had a huge old above-ground pool (not ever used) that we think harbored a large snail metropolis.
