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 with a bag, without any training or thought about 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 with a lifting capacity just over the item's approximate weight. Remember that the pressure on the bag decreases as you ascend, which increases the volume of the air inside (Boyle's Law), thereby increasing the rate of ascent. If a bag is selected that is too large and can only be partially filled, the expanding air will fill the bag more and more during the ascent, increasing the rate to the point 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 cause the bag to "burp," losing its air and letting the lifted object come crashing back down to the bottom.
"Burping" can occur when the bag is overinflated, as just mentioned, and rises to the surface too quickly, lifting the bottom of the bag out of the water and allowing the air to escape. The diver can also burp the bag by grabbing the 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, stop when it is still a little negative (not quite neutrally buoyant). The reason is that when you're ready to lift, you physically lift the item a few feet, then slowly swim it to the surface, controlling its ascent rate. As you come off the bottom, the item becomes neutral, and after a few more feet, it becomes positive. If you start out positive, your chances of having an out-of-control bag increase tremendously. The first diver photo shows 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 the rate of ascent using the bag's easy-dump or by burping it. If the bag gets away from you and goes to the surface uncontrollably, swim away from the area and ascend. Check to see if the bag burped and went back under, or if it's 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 used, the bag usually breaks free due to the extra air and shoots to the surface uncontrollably.
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 when you tow it 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 (with your octopus regulator or a low-pressure hose), always fill it 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.