I would drill a hole through both sides about 5 mm down from the top and either use a pin or bolt or even an electrical tie.
My mast gate went missing when the riggers were giving the mast a love job and I had to make a replacement. I found some sail track in the riggers yard and cut/filed and drilled it to fit. The underneath shape of the piece of aluminium means that it drops down nicely into the opening to keep the slugs from catching on any lips. I then drilled and taped some threaded holes in the mast for the retaining screws. I only needed one, as the slug entry on my mast has only been cut on one side of the slot. You would need 2 I suppose. The slugs slide freely past this section of the mast now.
Maybe you could do something like this. But if you need something that can be removed when reefing, then a bit of thinking a and a few beers may be in order. As I said earlier in my other post, the new main sail I had made up doesn't require the slugs to be removed for me to reef down. 
At present when l reef l just feed one down below the gate and drop out the next slide and pin the third, and it is enough to bring down the reef cringle 4 inches. That is all l need.
Sometimes just leave it as it is and live with a bit higher reef, but if l would be able to 'close the gate' it would just make me happier.
Wrestling it back into the track is the real pain, not dropping it. I use the Cunningham hook for reefing, so it is quick to reef down or shake out a reef.
Thanks for the idea.
Select to expand quotesirgallivant said..
At present when l reef l just feed one down below the gate and drop out the next slide and pin the third, and it is enough to bring down the reef cringle 4 inches. That is all l need.
Sometimes just leave it as it is and live with a bit higher reef, but if l would be able to 'close the gate' it would just make me happier.
Wrestling it back into the track is the real pain, not dropping it. I use the Cunningham hook for reefing, so it is quick to reef down or shake out a reef.
Thanks for the idea.
This would be an ideal time to lose the reefing horn and use either single or twin reefing lines and stay clear of the mast when reefing.
