I've spent some time experimenting with different ideas, and I've figured out a way to solve the problem I had with my watch strap, namely that it was very difficult to push the watch buckle's prong through the strap to close the buckle. Basically, I've come up with a similar weave, but with "holes" for the belt buckle. I haven't seen this pattern in my internet searches, so I'm calling it the "Derweesh Belt" or "Derweesh Weave". Because what the hell, why not.
Here's the basic pattern. I used the buckle from a women's belt (this
was originally meant as a gift) and a cheap carbiner to help keep the
cords lined up. This is actually a slightly tricky pattern if you're new
to weaving (not that I'm some sort of expert or anything), I would recommend starting with something simpler, like a
regular sinnet or cobra stitch.
1. Getting Started
Start by anchoring the cord to the belt.
Measure off the desired length and loop the cord back. I like to loop the other end to a carbiner, as it can easily be slipped off later, and fix it with an elastic band or a knot.
Bring the two strands back to the buckle. Note that one strand comes out from under the buckle and the other goes in from above, this is very important. Just to be clear, I shall refer to the four strands that extend straight between the
buckle and the carbiner as the spine or spine strands, and the two free
strands as the weaving strands.
2. Loop Back
I call this step looping back. Weave each weaving strand around the two spine strands on it's side, then back out, as in the photo.
Now tighten: hold or anchor the spine strands and pull the woven loops towards the buckle while pulling the weaving strands to remove the slack. In general I think it's a good idea to pull the weaving strands tight in this step to help pull the two central spine strands apart.
3. The Crossover
Now comes the crossover. Take one of the weaving strands and weave it through the four spine strands, treating the two central strands as if they were one strand. Don't pull tight yet.
Now do the same with the other weaving strand, but cross the first weaving strand while passing the two central spine strands, as in the photo.
As you can see the weaving strands have now crossed sides. Pull the woven loops down to the belt again, but don't pull too tight on the weaving strands this time or else the 'holes' in the belt will be too tight and closing the buckle will be difficult.
4. Rinse and Repeat
Keep repeating the crossover and loop back steps until you reach the end of the belt. As you can see in the photo you have gaps in the center of the belt where it's possible to push through the prong of the buckle. You don't have to weave one-to-one; you could use two crossover rows for each loop back row, or two loop back rows to make a larger hole that's easier to push the prong through, whatever works for you.
When you reach the loops at the end of the spine, slide off the elastic band and carbiner, keep weaving until you pass the weaving strands through the cord for the final time, then cut the ends off, melt the tips, and... do something with them. I didn't actually finish this belt as I soon realised that the belt was too wide to fit through the buckle. I'll need to get a slightly larger buckle and try again, then I'll figure out the best way to handle the ends of the cord.
This pattern has a few advantages. The holes for the buckle are the obvious one; there's other patterns that can work with a regular belt buckle but this is slightly smaller than some of them, making it just small enough for a use as a watch strap or women's belt. It's faster to make than a Slatt Rescue belt, even though you have to pull a lot of cord with each row you weave (though less than a simpler sinnet pattern as each strand has half the length - I recommend wrapping the cords around small spools the make it easier to pass them through the spine when weaving). It's thinner and arguable neater or more elegant than a Slatt's belt. Finally, you only need to deal with cords ends at one side, making it a bit neater to finish off.
The're some disadvantages too. It's a little tricky to weave; I've been having trouble getting the tightness consistant which can make it look a little messy. The holes are still a little hard to get a buckle prong through; you might have to sharpen it a little with a metal file to make it easier (I imagine they will stretch a little with use though). It's wider that a four strand sinnet (which is why I misjudged the thickness and found the buckle was too small). Unravelling it is also slower than some weaves, although that's not really an issue for most people.
Hopefully I'll use the pattern to make a watch strap soon, in which case I will of course post pictures.