Keith, the deer heard the car doors being shut and then legged it. I know the 7D shutter isn't the most quiet, but still...
I'm sure I'll be criticised for going round and into the fields, but I found somewhere to hide myself against a few tall bushes, and waited for nigh on 2 hours, watching the bird perch, swoop down, catch and eat, or return to its larder with prey, be chased by magpies and ignore both close-flying herons and buzzards.
When it finally did start to come within range, it was spooked by other birders walking straight at it. Before flying off into another field. After another hour, it returned to where it appears to roost, but chose to fly down the hill this time. Like other shrikes I've watched, it covers a huge area.
And then the hail arrived. Reward for standing in a marsh for hours... It doesn't "hide". It relocates. It's easy for it to be hidden from the road, as the field has hills and dips. When most people were scanning for it from the road, it was perched in a dip in the field in front of them, or behind the thorn bushes at the back.