Use 1 1/2" tape. Stick half of it down and fold half upward. Ot you can use the putty/tape that guys use to seal vacuum bags. I mix resin, 1/32" milled fiber and white pigment for leash plug and FCS fin plugs. I mix it thick enough that it doesn’t run. I rarely use FCS plugs anymore, unless I am repairing an old board for someone. Futures, Fusion and FCS iI, if done properly don’t have that problem