Moving Target
From the perspective of a tree-growing old bloke, with some practical experience of sending lead down-range, this problem isn't at all easy to fix. We already know (from tree damage, direct observation, dung counting, and so on) that we have too many deer in many areas in Scotland - the problem is one of control, not measurement.
Any 'credible predator' feeling peckish is probably more likely to take a swing at some local sheep rather than chasing deer for miles over rough terrain. That might get a few but probably not enough.
Shooting deer is not a particularly efficient way of controlling deer numbers. With sufficient firepower, equipment and determination, it can work well on open moorland, but is generally much less effective with deer species that prefer woodland cover (in Scotland that would often be Fallow and Roe deer).
Having been shot at, deer will typically 'up sticks' to another area and/or become entirely nocturnal. The whole enterprise then becomes *much* harder and more expensive.
And even in the event that SNH *do* get hold of some shiny new technology which churns out reams of accurate deer numbers (unlikely in the case of woodland-based deer), it is not at all clear what our next move would be.
Words like 'shark' and 'laser'come to mind, but then again.....