Use a Lift Bag

It takes practice to become proficient in using a lift bag! Is there a right way and a wrong way to go about it? Of course there is! The wrong way is to simply go underwater carrying a bag without any training or thought of how it should be rigged and used. When rigging and lifting an item off the bottom, there are a number of things to keep in mind that will make your recovery safer and more professional:

Do not use brute force to lift any object from the bottom.
Always use a lift bag or other salvage technique when the item weighs more than 10 pounds.
Never get underneath an item being lifted.
Never use your main regulator for filling a bag. Rather, use your octopus regulator (being very careful of entanglements and air consumption), a low pressure hose with an attached inflator mechanism, or a separate tank with an inflator device.
Try to use a bag that has a lifting capacity just over the approximate weight of the item. Remember that the pressure on the bag will decrease as you ascend, which will cause the volume of the air inside to increase (Boyle's Law), thereby increasing the rate of ascent. If too large a bag is selected that can be only partially filled, the expanding air will fill the bag more and more during the ascent and thus increase the rate to where the bag may become uncontrollable and shoot to the surface. This in turn could snag a diver and pull him to the surface, resulting in an air embolism or decompression sickness, or could make the bag "burp," causing the bag to lose its air and let the lifted object come crashing back down to the bottom.
"Burping" can occur when the bag is over-inflated, as just mentioned, and goes to the surface too fast, lifting the bottom of the bag out of the water and allowing the air to escape. Burping can also be done by the diver to deflate the bag by grabbing the bag's top D-ring or the top of the bag and pulling down sharply. This can be done during training exercises as well as during actual operations when you want a fast way to vent off expanding air or to dump all the air. Keep in mind that you can only burp smaller bags like a 100-pound lift bag.
When you're filling the bag, fill it only to the point where it is still a little negative (not quite neutrally buoyant). The reason for this is that when you're ready to lift, you would physically lift the item up a few feet, then slowly swim with the item to the surface, controlling its ascent rate. As you come off the bottom a few feet, the item becomes neutral and after a few more feet, positive. If you start out positive, your chances of having an out-of-control bag increase tremendously. The first diver photo show a diver using his octopus regulator to fill the lift bag. Notice the safe is secured with a 15-foot rigging line. In the next photo, notice the diver controlling the lift.
Stay next to the bag as it is ascending. This position allows you to control its rate of ascent by using the bag's easy dump or by burping it. If the bag gets away from you and goes to the surface out of control, swim away from the area and ascend. Check to see if the bag burped and went back under or is waiting for you on the surface.
Bottom suction can be a major problem. Quite often a diver will either have to dig around the item in the mud/silt, breaking its "seal," or overinflate the lift bag to overcome the bottom suction. When this latter procedure is resorted to, the bag usually breaks free due to the extra air and shoots to the surface out of control.
Rig your bag as close to the item as possible. This procedure takes a little practice but will allow the bag to lift the item close to the surface so that when you tow the item in, it will hit the bottom as close to the shore as possible (in shallow water). This will save you from dragging it great distances across the bottom and instead of having to get into water that's over your head to remove the item, you can walk in, bend over and carry it out.
When using the air in your tank to fill the bag (using your octopus regulator or using a low pressure hose), always fill the bag up slowly. If you fill it up too fast while breathing off your regulator, you can overwork your first stage and cause a free flowing regulator situation.

Two lift bag companies that I highly recommend are:

Carter Lift Bag, Inc. (My personal favorite) - Web: www.carterbag.com
Subsalve USA Division - Web: www.subsalve.com

Once again, the only way you're going to become proficient in light salvage, or any other law enforcement recovery technique, is to get the training and practice needed to allow you to participate safely and comfortably. So next time you make a practice dive, dust off your lift bags. If you don't own bags, buy some or borrow some.