dont cost much to rent weights from dive shop - call or email one aheadYou can carry your detector in a carry on, It will be treated as a laptop you will have to take it out of your bag and put it through the scanner. The rods and scoop have to be in checked luggage.
Once I had to turn my detector on to show it worked. Another time I carried my weight belt in my carry on with 8lbs of lead as my checked bag was at max weight, I had to leave either the lead or the belt as together it could be used as a weapon, I left the lead and took the belt.