I use Mk1 Eyeballs, scope, and the objects around me.
I have no place for an electronic rangefinder while hunting, as using one would undermine the test of one's self. Pest control on another's land is another matter, as their is a duty to be as effective as possible.
When hunting I am usually on mixed arable farmland, with most farmers using barbed wire with the barbs 4 inches apart, with 4 inch fence posts and 8 or 12 inch corner posts, with usually no more than 3 types/sizes of gate and 4 types/sizes of fence. Different fence types, some made entirely of wood, some with metal posts, some with hawthorn or blackthorn, all have different standard widths/heights or sizes of objects within them. Trees of various types grow to maximum sizes, with some sizing/spacing of twigs and leaves being common. I find cattle and sheep a little problematic, but horses, grasses, wheat, barley, oats etc have some common sizes at various stages of development or time of year.
I know all the horses heights in cm, which helps me a lot in range finding while shooting rabbits in amongst them.
Easiest and quickest of all is the creature themselves. Once you get a little experience of shooting you can look at a rabbit, woodpigeon etc and know how big it is and so quickly calculate its range.
