Hi Dave, there are ways to reduce the risks, but not eradicate the problem, you'll have to do the same as the rest of us, and live with it. For what it's worth, here are a few ideas;
1. Computer disks hung in the garden
2. Mirrors to reflect hawk's own image - they don't like their own species.
3. Let the birds out at different times, so the hawk is uncertain of prey availability times. It can't hang about all day when it may have hungry chicks to feed.
4. It is said that birds with white rumps offer confusion to an attacking bird of prey, this is a quite predominant colouring in pigeons.
5. Some birds of prey locate targets from a height, then move in from a distance at a lower level. Try not to leave the birds out scratching around for too long or if you do try to stay with them. Hawks are shy of humans, (although increasingly less so).
6. Don't underestimate the role of wild birds, they nearly all have their own early warning signals which the pigeons soon recognise.
7. Don't let less agile pigeons out, ie stock birds, tired racers, injured birds etc. The hawk is a master at picking out the more vulnerable bird.
8. The hawk will often hunt straight after rain, cos'. a) It hasn't been able to hunt itself, and It knows many of the wild birds need to come out and feed, and that feathers may be drenched, making them easier targets.
9. If you are going to use dummy eagle owls, make sure you take them in when you're birds aren't out, and keep moving it's location in the garden
It is a fact that some of your birds will fall victim, but it's a great sport and worth some of the heartaches.