All options below are great for containing leaks as well as smells. Always be sure your current cloth or disposable diaper is the proper absorbency for your needs BEFORE adding a "leakproof" and "smell-proof" cover.
Vinyl plastic covers like the Protex "Tuffy" Collection are made of THICKER plastic to better contain odors. Tuffy covers are lightweight even with the 7 and 8 Gauge vinyl.
Rubber covers are the best option for odor control, but do have their own "rubberband" scent, as they are made from natural rubber. Rubber covers such as the "Long Bloomer" pant can be heavy as they are made from more material.