I found this book at Peg Leg Pub on Simpson Bay in St Maarten, the Caribbean. They have a great selection of books for swap - one to one.

From the back cover:
The old wozard wasn't happy with Valder, who led the enemy to his hut. Now hut and magical supplies were distroyed. But he'd promised the young army scout a magic sword to get him safely back to his lines and a much enchanted sword Valder would get.

The resulting sword gave perfect protection -sometimes! It could kill any man-or even half demon. In fact, once drawn, it had to kill before it could be put down or sheathed.

Army wizards told Valder that the sword would keep him alive until he'd drawn it 100 times, then it would kill him. If his new job as Chief Assassin for the army didn't make him use up the spell, he'd be practically immortal.

Not bad, it seemed. But there had to be a catch somewhere and there was!

RELEASE NOTES:

I didn't get to read this book but need to clean out my bookshelf and so am passing it on.