Step 1: Getting what you need
The radio control and propulsion are from a toy Jetski. These are available in toy stores like KB-Toys. They sell for $19.00, and are easy to dismantle. I found two more in secondhand store toy bins, so don't be afraid to check there too. (E-Bay too) There are other toy boats that could be used, but I like the motors underneath. They allow for differential steering. Without a rudder, it becomes less complicated to rig a duck to steer. The motors run independently, both on for forward, left on to turn right, right on to turn left. It will rotate in place, so its easy to keep a baby duck in frame, and is quick enough to follow a family around the lake without their attention. The Jetski is from a company called Echo, and uses a radio frenquency of 27mhz. Range is a bit restricted, about 100 feet, but on a body of water thats pretty far. You could easily install a more powerful RC and electronic speed control, but costs will really run away if you do.
Last is a duck decoy, and you will need two. Males and females are available in nearly all species. I chose a Mallard male, and somtimes tow a female behind. They cost about $4.00 each, and are made by a company named Flambeau Products. They are available in sporting goods and hunting supply stores, online and mail order. They are a bit seasonal, but not too difficult to find. I purchased two for $3.99 ea. The reason for two, is the first is cut open with and oversized opening to cover the back of the second, to provide enough overlap that it becomes somewhat water resistant. This may seem a bit wasteful, but they are inexpensive, and its too important that you protect the camera from moisture.
The extra decoy makes a great planter, or use it as a pencil box on your desk or maybe a cereal bowl or even a dog dish!
Thats it! Simple tools are needed, a drill, and a Dremel tool is handy, a few connectors, and some NiCad batteries. (A broken hacksaw blade cuts the back easily if you don't have a Dremel.)