I might be able to help you with this - we have plantations and run sheep in them.
First of all, if the trees are small (under double the height of sheep), the sheep will browse they tips. Sheep prefer vines, young trees, and many weeds over grass. You can fix this problem with netting, use three poles and make sure to cover the tip (use open netting). We actually use sheep to keep down brush and vines - so you aren't going to teach them not to touch the trees.
Secondly, if you are having problems with the sheep eating bark, it is almost certainly due to not having the right minerals - or too many males. You
should have more than one ram until you get past 40 sheep. (rough numbers) More than that, and they will start showing dominant behavior, which includes destroying trees.
Sheep really don't use grain, what I would suggest is putting the grain where only the geese can enter (make a small entrance to a
chicken wired enclosure.) If you do something like this for lambs to fatten them, it is called a creep feeder by the way.
Sheep really don't drink that much water, but geese want to play in water. Not sure how to cure this one. Geese and sheep might not be a good combo.