a single antenna is fine but you have to be able to read "spikes" at a depth of say 4 feet an analogue box will give you FIVE points with the SAME strongest signal.
With practice,practice and practice it can become second nature But...................
you have to work in a grid like pattern, up down, left right, repeat,repeat until you plot out the signals you are getting back.
if you imagine a clock you will get a weak signal at 12, 3,6 and 9 o clock
The dog is right at the centre of the clock and you'll get the strongest signal there.
But you'll get a similar strong si