[skimoose]

According to the link you posted, the fins are precise cut plywood. I'd go with the epoxy. To reinforce the joint, you can embed some fiberglass window screen material into the epoxy on both sides of the fin similar to fiberglassing something.

Mix your epoxy and apply to the both sides of the break. Place the fin back on and then apply more epoxy to each side of the fin and body tube and press the window screen into the epoxy across the break so that its tight to the fin and body tube and the excess epoxy is forced out through the screen. Then use a piece of scrap 0.020 plastic sheet or index card as a squeegee to spread the epoxy out in a thin layer over the screen and remove extra epoxy.

Next, use masking tape or your favorite method of holding the fin in position until the epoxy cures (24 hours), but check it a few times before the epoxy sets to make sure the fin is still straight. After curing, trim any screen overhanging the fin, sand lightly and your repair should be good for launch. If you want really strong screen, Home Depot sells screening which is labeled (I think) "Dog Proof". It has extra fiberglass strands or Kevlar strands embedded in the product.

Also, if this fin broke off during a landing impact, you might want to consider applying a fillet of epoxy to each fin where it joins to the body tube to strengthen all the joints.