If you frequently fish close to snags, like the post you mention, you need to be fishing pretty well locked up, ie with no free movement of line from your reel, and always stay close to your rods as they can get pulled in! At night, don't even think of zipping the bivvy door up........
And you're right, under those circumstances you need immediate hooking of the fish so a fixed or semi-fixed rig would be my choice, too.
Ian