Hence Sauron and Morgoth's reaction to a wolfhound who cannot be slain, save by the greatest wolf that has ever walked the earth, which is basically : We're Going To Need A Bigger Wolf.
I was thinking about that this morning while making coffee, and particularly about orcs. Orcs cannot abide the Sun. It's not just that they hate it, it appears to be physically impossible for them to operate in sunlight for long. Until Saruman got to work on them, at any rate.
But why? Surely it is monstrously inconvenient to have a workforce and army that can only operate at night? Saruman clearly thought so. In Northern latitudes in the summer, the hours in which they could be in operation must have been annoyingly short. But if it is possible to fix this, whether by genetic engineering or by blending the races of Orcs and Men, why didn't Sauron do this previously? He had thousands of years to work on it.
I have two possible theories :
1) Sauron considers the technical specifications of Orcs, as created by Morgoth, to be in some way sacrosanct. Possibly fiddling with them is forbidden under a license agreement. The fact that Orcs seem to be degrading and becoming less and less effective as a fighting force over the Ages is no doubt a source of much woe to him, and he probably spends a lot of time virus-checking them and defragging their hard disks.
2) Sauron thinks on a grand scale. He confidently expects the Great Darkness to return at any moment, and can't see the point in carrying out fiddly small modifications to fix what is clearly a temporary problem which will soon be fixed by large-scale modification of the environment. Saruman's orc-modification program, to Sauron, is like someone who makes a channel for the stream that is annoyingly flowing through their living-room, whereas Sauron's approach is to simply re-route the watercourse.