I reckon they might obscure enough to make it more difficult to hit, but not to save against. So I would give the -1 to hit, but not the +1 to the morale save. Also remember that the fence would remove the charge bonus of +1 to hit.
"Right! Open this door or I'll take away every piece of Warhammer you've ever owned!"
The rule book (QRS under morale) mentions both light cover and heavy cover. Light cover is "hedgerows or similar". Is a fence similar? I was at Gettysburg this summer and the ranger said they counted 800 musket balls in one one rail of a rail fence at the angle. Was that cover?
What about fences and stone walls causing a target not to be clear? If not clear then it's a +1 to hit. If its light cover then it's also a +1 morale save. So that would be 5+ to hit and 3+ to save with a 4 morale stat.
Also if fences and stone walls cause a target to be unclear (not as visible) what do you guys play as far as definable position? Directly touching the obstacle? Within one base width? Or just define these details at the start of the game and agree on them? The rulebook is somewhat loose (or flexible) on these things.