The best place is on the Cairngorm plateau for both species, but breeding numbers of Dotterel are declining due to disturbance by walkers and birders who are forced to walk up the well laid out paths since the chairlift stopped and the authorities won't let anybody out of the funicular.
Walkers, in fairness, tend to head straight for the peaks, and stick to paths, but birders, in our excitement wander about like headless chickens, treading on nests and scattering the sitting males.
So, please tread carefully. Literally.
The best advice is stick to the paths, scan regularly and listen out for them. By July there should hopefully be no more birds sitting or feeding the newly fledged, they should all be up and running, which makes life a bit easier. Having said that, the last two years have seen all the birds go by the end of July, 2002 they were washed out, and last year the weather was so good they had fledged and flown in record time.
Despite the walk up, which can be long and arduous, when you see them it really is worth it, and if you take photos, don't forget your camera, because they aren't overly shy......
Anyway, hope the weather stays good for you and you do see them.