One other solution, not so bad =>
1) using a random box
2) using barrier tactic
3) put a 5 or 7 miles tolerance to the barrier WP
why barrier ? because during the barrier, the sub will periodically come back to the link, to send or receive data.
This period is very variable, sometimes 30 minutes, sometimes 1h30 ... it's just never the same.
So the sub will stay at the desired depth, and sometimes will move up just under the surface, using antenna or floating wire to come on the link for 5 to 10 minutes, then will go back to his assigned depth.
With the random box (or dynamic locations, even better) and the tolerance, you couldn't know where the sub will spawn neither what will be his exact course (you could have 45° or even 90° of incertaincy if you want, just increase the tolerance or reduce the WP distance).
If you also create random depths change during the mission (using whales as said MaHuJa), random initial depth (using 3 dynamic group at mission start for 3 different depth, it's really easy) and speed (as easy), you could have quite a large number of differents barrier patrols with only one programmed sub.
here is a example of scenario with random speed and depth
=>
http://okof4.free.fr/missions/DW/MP4...slick_v1.02.mu
the HAN and the XIA are scripted to have random speed (4 differents, but same for XIA and HAN) and random depth (3 differents, XAI and HAN independent) at mission start.
this give you 36 different configurations !
With only quite a few work (only 4 scripts for speed, 6 scripts for depth), very easy to elaborate and quickly built (30 second each), and some dynamic groups to make it random.
It's often better to script a single sub than to use many different subs when you need to assign triggers to this sub (destination / kill etc ...).
It save LOTS of working time, for a more random choice than just creating different "static" (I mean not using random settings) subs.