The best thing you can do around the house is cover things that have holes with window screen, avoid creating possible nesting sights(stacks of tires,or junk)be alert and check your property often. All of these things will limit the chance of your dog having a run in with africanized bees. If attacked,cover your head and don't stop running until you reach safety.
Here are a few links to information about africanized bees. Add .html to the end of this one http://www.desertusa.com/mag98/sep/stories/kbees

Here is a link that might be useful: http://honeybee.tamu.edu/safety/index.html

I think you are the victim of some misinformation here. Yes, the africanized bees are very defensive but no, they don't go out and hunt down barking dogs to kill.
A foraging africanized bee is no more dangerous than a european bee. The difference is that the AHB is much more defensive of their home.
Home is the key. Like Tony said, keep probable nesting sites to a minimum and you likely will never have a problem. If you do see lots of bee activity in a possible nesting site all of a sudden, don't wait. Call someone emediatly. You have a little time before they become aggressive. They can be removed or killed relativly easily if you catch them before they settle in and raise young.
All in all, if your dog is just running around your yard barking, you don't have much to worry about unless there is an established hive within one hundred yards or so from your home. Your dog has a greater chance of getting out and getting hit by a car.

tonybeeguy: did you actually read that first link you posted?

"Though their venom is no more potent than native honey bees, Africanized bees attack in far greater numbers and pursue perceived enemies for greater distances. Once disturbed, colonies may remain agitated for 24 hours, attacking people and animals within a range of a quarter mile from the hive."

So, while I take all precautions I can in my yard and around my house, I can't prevent an agitated colony from descending on my yard and attacking me or my dog. Which is why I am looking for a defense mechanism to combat the bees should they attack my dog.

Again, any ideas on foam or soap sprays that would be effective?

Yes, I did read the information on those sites and have seen videos,heard people speak and read books on Africanized bees. Some beekeepers who work on africanized hives wear double suits and duct tape every opening where a bee might enter. In the case of a feral hive attacking, I wouldn't want to go up against them without proper protection. The only think I can think of that may have some effect would be a large c02 fire extinguisher, but keep in mind if the bees were attacking your dog and you ran out there, they'd be on you in a second, and the only practical way to defend yourself is to get away.Maybe you could leash the dog from inside, so you could at least pull him back to the door if need be, and hit the bees through the screen. Note that the way an extinguisher works is replacing oxygen to smother a fire so it could also suffocate a dog or person if emptied in their face.
I don't mean to downplay your concerns;ahbs are here and the threat is real, but the best defense is still educating EVERYONE on precautions to take, reporting any new nests and having them removed by qualified people.

Thanks for the response, tonybeeguy. Unfortunately, my dog is 55 lbs., and it would take quite some time to drag her back into the house. I now stand and watch her every time I let her out, instead of letting her out to roam in the back yard as she wishes. Maybe I'm paranoid, but I've seen more bees around my house this summer than any other summer. No, no nesting that I can see, just bees in general flying around and doing their thing.

One thing I did notice, which is weird, was a bee buzzing around my patio light last night at 10:45. I thought bees were back in their hives at night. This might explain why I have found three bees dead on my patio in the last few weeks. And only when the porch light has been left on overnight. Why are they out and about after curfew (hahaha) and why are they attracted to that patio light?