How to use a marker buoy
Working with a marking buoy underwater takes practice and concentration. Many divers have learned the hard way that using a buoy for the first time can mean entanglement, free buoy line floating all over the surface, or loss of the buoy. So don't wait until there is an actual recovery operation to practice your buoy deployment. It's not as easy as it looks, especially when you take away visibility and put on a pair of gloves.
Securing the buoy to the diver
I personally do not wear a marker buoy on the outside of my equipment like a grenade. It gets in the way and the line likes to come undone and get entangled with everything, including me. I dive with a goody bag and keep one inside or place one in my BC pocket.
If you do wear it on the outside make sure the buoy is properly secured to you before entering the water. This can be done by using a snap hook on your weight belt or your B.C. (if you have one there) or by using the buoy's own securing device (if it comes with one). If you're using a snap hook, make sure the hook can be opened with one hand and is of good quality. Many buoys come with less than a perfect hook, one that you might need to replace before taking the buoy into the water. And be sure you secure the buoy to you in a location you can quickly and easily reach.
After you locate the item you've been searching for and you're ready to work with the marker buoy, move to a position directly in front of the item and unhook or take out the buoy, never letting it leave your grip. Undo the weighting system by unraveling 2 to 3 feet of line, which will give you enough free line to work with. Then secure the weight next to, under a rock for added weight, or around the object of your search, or you can even attach it directly to the object. The securing method you use depends on the object, current, depth and your chances of losing evidence. Be careful not to let out too much line when securing your weight, because it can easily become entangled with your equipment and you yourself.
Throughout this procedure, one hand is securing the weight and the other is holding onto the buoy. If you need both hands free to secure the weight, you can place the buoy in your armpit. Do not let it go to the surface yet.
Releasing the buoy
You should release a buoy only if and when you yourself are ready to ascend directly below the rising buoy to the surface. The main reason for this precaution is that once the buoy has reached the surface, the buoy line will reel itself out by force of the current or of just your exhaust bubbles hitting the surface. The extra line that this creates can get caught in your equipment or simply cause drag, either of which conditions could result in the weight or item being moved. If you are diving with a buddy, one of you may choose to stay with the located item, depending upon what procedures you agreed to before getting into the water. After you have secured the buoy, slowly release the buoy and allow it to ascend to the surface.
Is there more to learn about using a marker buoy? You bet there is! Unfortunity I don't have the time or the space here to write it all down. I hope this little bit helps you in some way. Good luck in your search and recovery diving!