@Nicholas,
Zip tie looks OK, but I don't like the idea of tugging against the device to tighten it.
A SHCS, and nut with a hole through the head of the screw.
Turn the screw to take up the slack, then lock it down with the nut.
I like the SHCS because I can easily adjust it if I felt it needed inspecting.
An eccentric cam.
A leaf spring, low profile, light weight, high force.
You could also attach the string to a cam, which would push on a coil spring to increase the rate of force.
A2
Zip tie looks OK, but I don't like the idea of tugging against the device to tighten it.
A SHCS, and nut with a hole through the head of the screw.
Turn the screw to take up the slack, then lock it down with the nut.
I like the SHCS because I can easily adjust it if I felt it needed inspecting.
An eccentric cam.
A leaf spring, low profile, light weight, high force.
You could also attach the string to a cam, which would push on a coil spring to increase the rate of force.
A2