How about a;
Station Master Pro? Check the circuit/short/solenoid, etc. Every irrigation pro ought to have one. (Even comes with a noise maker to track wires although it is useless on a long run). You can operate it right from the controller or even out the field.
A real wire tracker & a 5ft. 3/8 - 1/2" copper grounding rod hammered down to the nub with an UBER clamp & at least #12 wire?
run it until the signal gets weak, dig up the wire and hook it up again there and move foward. ( be sure to splice the wire back together when you finish... duct tape is good for that right?)
16 Guats with probe rods?
Site map with valves located on it?
Hammer SCD40 piece of pipe within pi$$ing distance of the valve with so much metal in it a $20.00 metal detector will find it. & make sure the field box doesn't get grown over?
I complain bitterly when the LCO (unless it my Co.) lets crap build up and cover the field boxes.