Soaking isn't realy very effective if it's good resin. Considering that some of the resins used for fiberglassing boats are among the best waterseals/moisture-barriers that you can find for wood, they aren't likely to budge if the job was decently done, and you can leave most fiberglass submerged for years and when you take it out, it's still fiberglass. Don't expect it to wash off or give up its grip on the wood fibers from a little water-soaking, because it's not likely to happen. The wood will rot away first.
Carefully applied heat and elbow grease are the only effective ways to remove it. You need maybe 140 degrees to begin softening most epoxy resin and likely a bit more for polyester resin. The epoxy sticks better from the get-go, so despite needing less heat, it may be considerably more work to remove.