If you are busted/spotted on a stalk, don't immediately drop out of sight. If the sheep don't flee, sit still and wait. You may be able to resume the stalk out of sight if ignored (unlikely). If needed, slowly carry on towards them, or angle closer to try to get in range. If you are spotted and you drop out of sight, usually they get nervous and leave.
Always be cautious of any objects in your posession that may reflect/shine. Glare off a glossy barrel, rifle scope, fancy sun glasses, binos etc can be seen for a LONG WAYS, and will make you stick out like a sore thumb.