I don't think shorter shields would really solve anything except making it even easier for people to avoid combat with people they may actually be evenly matched with. I can't say what percent of people do this, but I'll hazard a guess and say that the majority of players seem to enjoy demolishing the towns of people much weaker than them and then shielding up before there could possibly be any retaliation, delivering cheap shots all day every day while shoving this "shield or die" agenda down the throats of their unfortunate victims.
Keeping in mind both paying and f2p players... When considering the hefty cost of resurrecting troops as well as the lengthy processes of plundering or yielding huge sums of resources for upgrades and amassing a formidable army, it's no wonder why so many people choose to take very little, if any, risk in this game and a gaming session can usually be described as either dull or infuriating. What would be most helpful is an alternative combat option, some kind of PvP where players could challenge one another in a way that would allow them to send only as many troops as they'd wish in a match that may cost them a percentage of their resources instead of their entire army and resource supply. That could at least lure some people out from under their shields and promote a semblance of sportsmanship. Just one idea.
My point is, I don't think we should encourage this one-directional gameplay by making it easier for people to shield up after every march. If anything, shields should have a MINIMUM of one hour after applying a new shield before you can choose to drop it again.