Many procedures are discussed in the literature or online for repairing aluminum hulls. It appears to be generally agreed that fiberglass is not appropriate since it does not flex as the aluminum on the hull does. Aluminum brazing rods, which can be used with a regular propane torch, are also advertised. Feedback on boating forums seems to be divided on how well these work and what expertise is needed to accomplish the repair. I have not used these personally. Other approaches that could also be tried are JB Weld epoxy and applying paint on truck bed liner available in auto parts stores.
One compound that seems widely used is 3M 5200 sealant. The surface of the aluminum and rivet should be cleaned and the sealant is applied much like caulking. It forms a durable patch that should last years. It comes in a regular and fast cure format in 3 ounce and caulking tube sizes. One word of caution is to not buy more then you will use at one time since once opened it will cure in a day or two even if you reseal the tube.
Another approach to repairing a leaking boat is sold by Cabelas Outfitters and is called Cabela's Aluminum Boat Patch. It is applied to a clean aluminum surface with the use of a regular propane torch. It can be somewhat inconvenient if the leaking surface has been painted since this will have to be removed with sandpaper or a wire brush. The area is heated with the torch until the stick of solid sealant can be wiped on. It can fix small holes, leaking rivets and cracks. Once the boat is demonstrated to be leak free it is possible to paint over these patches if desired. It is only 6.99. I gave you the link.
http://www.cabelas.com/prod-1/0001390010655a.shtmlA leaking boat is a nuisance and reduces the enjoyment of boating or fishing. Several easy to apply sealing options are available that should provide durable patches when applied properly. Part of the challenge in repairing a boat is to find the exact place where it is leaking and being able to reach it to clean and apply the patch.