time travelling wazd! thats great
overhead will work better for a simple style game.
if you could remove the gate however and have that as simple transparent pngs or svgs then they can be laid down as required.

level 1 1 sheep, 1 gate, 1 dog 1 sly fox randomly appearing
level 2 2 sheep, 2 gates, 1 dog 1 sly fox randomly appearing
level 3 3 sheep, 2 gates, 1 dog 1 sly fox randomly appearing

etc

also, does it specifically need the accelerometer - i know it will be good, but could something similar to this be played on the n8x0?
would be nice to see if there is a playable variation for all devices