Soulbound, a very OP enchant that serves to keep your item. It should be one-time and made double the price so that way you have to grind for it and then you lose it. It would be like an extra-life, but for the sword. Once it is lost you have to grind for it again. Thus having to dedicate yourself to it, so not all pvpers will have this enchant and will be a rarer thing.
There is another approach you can take. You could make it so you have a 70 percent chance of keeping it, that means you have a 30 percent chance of losing it and is permanent (The enchant). I have stated 2 ways to fix the enchant.