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