The commando promotion doesn't seem that useful. It comes so far into the promotion tree that you'll likely never have a newly built unit able to take it right away. That means you'll need an experienced unit to have it, and because of what the promotion does, that would mean you'd be leaving that unit alone in enemy territory and you're sure to lose that high experience unit. I was atching TV and saw something about paratroopers securing roads in Germany in WWII and that got me thinking about having a promotion that lets your other units use the road it's standing on? There's still the problem of requiring several of them to be effective, but it wouldn't require all your units to have it.