I have Strap extension Which is just like Above, but it's the same as the strap I have on my comp. If I forget it though I just put it around my Depth gauge on my SPG and just have it on there tight (with a clip on the top of the SPG connected to my BCD incase it does come loose and slide, but it hasn't).
But then again that's a Computer. In the case of your watch, I'd strap it to a D-ring, put it to the tightest notch, and make sure the extra strap is secure under the watches keeper.
But then again that's a Computer. In the case of your watch, I'd strap it to a D-ring, put it to the tightest notch, and make sure the extra strap is secure under the watches keeper.