The prevalence of heartworm depends on geography not just mosquitos, check to see if there is a high incidence among the population. All of the dogs I've had had been on HW meds because I live in an area that has lots of mosquitos and a high incidence of HW. I've never had any problem with it.
You can also opt not to put him on HW and have him tested every year, but if he does develop the protocol is much longer.
You got a nonsense response about lower forms of life and electromagnetic spectrum. You should ignore it as it has no basis on reality. Nice buzzwords but if you actually look at the meaning you will find none.
Free choice food is generally considered to be bad as it promotes obesity among our non-working dogs and it will do nothing in terms of preventing HW.