How about a removable skeg? I have an old wakeboard with a removable skeg. I took it off to make a sled. Not sure where the skeg is now, but it's about the right size. It was attached to a mounting plate that's flush, with some phillips head screws. BTW, if you're sledding on a wakeboard, be sure there are no trees near the intended route... Kinda hard to steer...

: Before i built my first kayak, nick had just completed his, a boat now named
: "great auk" he and i whnt for a paddle, i just had his leaky old
: whitewater kayak which i couldn't keep straight for the life of me so i
: duct taped a peice of aluminum rain gutter to the back and headed out. it
: sure was ugly but it worked.

: ive seen some plastic boats with removable skegs mounted on a ring which fit
: around the stern and was held there by a lanyard or something...you could
: easily do that...it will work.

: --eric