Turn Townhalls into command central.
One easy way to cut back on farming would be to force people to protect their Townhalls and not pick up easy shields. Why not make the hall like a command centre that if taken out the remaining defences become confused / panicked and their effectiveness is reduced by like 50%. So if you just leave your hall unprotected it will be taken out first and then the rest of your layout will be much weaker. You could also make the percentage of the amount you loot go up if the hall is taken out. Force people to protect the townhall or as I would like to call it : command central.