No way to prevent it evolution of disease

I just finished reading quite a few interesting articles on dogs and heartworm medicines.  Turns out they are finding cases of more and more dogs who are on regular (year round) heartworm medication and still catching heartworm.  One of these documented cases was a veterinarian who was giving his dog two doses each month because he was well aware of the possibility of the medicine not working.  This isn't a select few of the popular heartworm meds out there, it's all of them.  I know they're bringing back the heartworm medication that is given by a shot once every six months but it sounds like it's going to be very strict.  I personally, wouldn't use it as I was around when it was used popularly and witnessed dogs die from this medication.  Many vets think the risk is worth the wonderful coverage that ProHeart-6 provides but I'm not putting one of my dogs at risk.  I personally use a solution that is given once monthly based on the weight of the dog.  It is not something the vets openly use and if it were found out, I would probably be in trouble.  Any mix up with dosages could kill your pet and it is the large reason why I do not disclose what the medication is or how you can obtain it.  Even this is not considered 100% anymore.  I wonder how many people felt cheated by their veterinarians and the manufacturer's of these drugs when their pets still came down with a heartworm infestation?  I was unaware that this was possible until recently and even then I hadn't yet read of documented cases.  How do we keep our pet's safe?  It's so very frustrating.  I try not to leave my dogs out too long after it gets towards dusk when the mosquito's come out in hoards.  Other than that, I have no answers and I don't think the vets do either.