Yep, it really depends on how much time the unit spends in one place. The more time that passes, the more obstacles that would generally be constructed. Of course in modern warfare, usually a unit doesn't sit around in one place very long though.
However, for the sake of scenario design rule of thumb, I'd say that for a Mech Bn, you'd figure that each company would have at least 1x and usually 2x, and at most probably 3x minefields to deploy, if you don't want the entire front line a solid belt of minefields.
Then after that, about 4x to 6x single strands of wire per non-command non-support vehicle (in other words, per front line combat vehicle). Then take that total number per platoon and divide by whether you want double or triple strand wire obstacle (or not if you just want single strands). So, for example, using 6x strands for each combat vehicle that would be 6x single strand wire obstacles, or 3x double strand wire obstacles, or 2x triple strand wire obstacles. Then include vehicle emplacements (one for every combat vehicle, and at most two per, to allow alternate position - but that is a luxury) and you have a very good deliberate defense situation. Then you can possibly allow them to all be deployable in company sized different color deployment zones to increase the Planning Phase "fun".