We recently hung four large (approx. 7'x10') watercolors. The artist wanted them hung with only one nail in each of the top corners. (I know...) To do this I laminated squares of #300 watercolor paper to the back of each corner with PVA adhesive. These held the weight, but as the paper has moved (expand/contract) due to our imperfect climate control the paper is very slightly tearing- but it's tearing left-right, not down. I tried replacing the nails with linen-lined binder clips but they are not strong enough to hold the weight, so I don't think RE magnets will cut it either.
What other options are there short of putting more nails through the top edge? Is there a material I should've used besides the #300 paper?