I'm a new user, and an on-again-off-again crappie fisherman. I've had a couple ideas for new (at least to me) potential structures that I thought I would share and see what people thought. Let me know if you have any ideas or comments.

Kelp Bed Structure: This is a series of anchored, floating structures which "sway" in the current, kind of like Kelp in a kelp bed. At one end is a weight (a rock, chunk of concrete, sand bag, etc), say roughly the size of a beer can. Attached to the weight is a long, narrow strip of some material, say 3-6" wide and 3-6' long. This can be made out of just about anything, cheapest being a roll of heavy duty plastic sheeting or tarp (*NOT* garbage bag), but I think the best and fastest producing would be something like burlap (cheap by the yard at Walmart, free if you can find burlap feed bags or coffee sacks being thrown away). At the other end is a float, buoyant enough to keep the material vertical in the water without lifting the anchor weight. An easy one would be a 4" long piece of PVC capped at both ends and attached with a squirt of Liquid Nails, but you could really use just about anything; you can even make them all natural with burlap and some sort of natural float like sealed balsa. To deploy, you roll the strip up around the float like an Ace wrap, leaving the weight free. When you drop it over the side, it should unfurl. The idea here is fast, cheap, and lots of them. You can "cluster bomb" them over an area to build a bed; works especially well for "stealth" emplacements, no one wondering what that thing is on your boat at the ramp.

Hard Kelp: Like the kelp, only using capped PVC. Take a length of PVC, cap at both ends. Attach weight to one end via whatever method you like. Make sure the volume of the capped PVC is enough to float it upright, but not enough to lift the weight. Take up little room on the boat, easy to deploy.

Easy Concrete Weights: For non-load-bearing structures, like making weights, it is much easier to deal with dry concrete and hydrate it afterwards. Concrete made this way is still seriously hard, as anyone who has left a open bag of concrete out in humidity can attest. Easiest way of making weights is to dig a series of depressions in the ground, poke a loop of tie wire into the bottom, fill with dry concrete, lightly water once or twice, then let sit for a couple of days. The same can be done with plastic cups, sand, etc. To make anchor legs, have extra lengths of wire poking out of the top that can be bent into legs or hooks

Fake Stump: Similar to the Kelp, only bigger. Take a large shallow plastic tray (like the kind used under potted plants), fill with concrete, embed a group of tie wires in a circular pattern. Take a length of material, say burlap, around 2x4'. Fold over a couple of inches along the long side and sew (could also use weatherproof adhesive) like you're making a drawstring bag. Then sew ends together to make a tube two feet long and a little over a foot in diameter. Make a ring float by taking a length of black plastic garden tubing (the kind used for irrigation), feeding it through the overlapped part at the top of the burlap tube, and connect the ends with a barb fitting. The bottom end of the tube can be reinforced with a loop of wire, then tied into the wire ties in the concrete base. Holes can be cut into the material to provide additional access and hiding places.

Crappie High Rise: An individual floating structure. A heavy weight on one end (concrete block) tied to a larger float (bleach bottle) by a piece of poly rope. Threaded on to the rope are large rectangular pieces of stiff material spaced out by knots. After thinking about this one, I think the best material would be the plastic corrugated "cardboard" used for roadside signs, like the kind used by politicians and home builders.

Bonus: a good material for building impervious cluster structures is vinyl vertical blind slats. They're not too expensive new, even better if you can get them for free from a remodel. Nice, flat, lots of cover.