Keep in mind not all meteorites can be picked up with a metal detector. If it left a crater like you say then there's no need to use a metal detector. Walk out to the crater, locate the meteorite (don't it touch yet), get a digital camera and take a picture of it right next to the GPS with the exact coordinates showing. Then pull the meteorite out of the ground and take another pic of the indentation with the meteorite right next to it. This gives the meteorite provenance and proves the exact location where it was found by documentating the recovery.
After getting it out of the ground, store it in a dry place and try to not touch and handle it as much as possible. If you want to touch and hold it wear some gloves or something because the oils from your hands can affect it. For storage keep it in a closed container with bags of desicant to keep it dry. You might also want to look into classification to prove it's a meteorite.
If it's fractured in anyway and it looks like it might have broke into other pieces, then there's a very good chance there will be others around.
Another thing- you might want to recover it ASAP since weathering can destroy it. The earths environment is considered a hostile environment for meteorites and oxidation starts to occur as soon as the meteorite enters into the earths atmosphere. The earlier a meteorite can be recovered the better.
I hope this helps, good luck!