I was just commenting the other day that our sheep are so good with baa-ing. The only times we get baa-ing outside of a problem is if we have been feeding them concentrates or if we are weaning. Any other time if we hear baa-ing it means something is wrong, a gate has swung shut separating the flock, the grass is getting too low, someone has gotten themselves stuck in the polytunnel or, as we found the other morning, a sheep has gotten itself into the back garden and can't get back out again.
If I wake to the sound of baa-ing I get a sinking feeling before throwing on some clothes and heading out quickly.
Not sure they will do what you want them to though. My husband just cut down some 8ft thistle trees in one of our fields. You'll still need to do a lot of maintenance on the field and you'll need to do maintenance on the sheep (twice daily checks, BCS, worming and fly treatment when needed, investigating lame/ill sheep, potentially tupping and lambing, shearing). You may find a field of sheep is more work than your field is currently. That said I love our sheep, I love the meat we get from them. Just make sure you're going into it for the right reasons. A course would be really good idea.
Dans