Yup. Sticking to insults works.
To clarify what you can safely say about the superintendant:
If you read a news story that says the superintendant is under investigation for accepting kickbacks and for nepotism, the most YOU should say is "such-and-such newspaper reported that the superintendant is under investigation for accepting kickbacks and for nepotism." That is all YOU can prove as true. That is the extent of your knowledge.
You do not
know that he is corrupt, although that may be a fair conclusion for you to draw from the news coverage. To be legally safe, let your readers draw those conclusions. Do not draw the conclusions for them. For you to SAY the superintendant is corrupt is to go beyond your personal knowledge and experience. Your words can "convict" him, when it very well may later be determined after the investigation that there is no evidence to support such an assertion after all.
You can state pure opinions that are neither proveably true or proveably false, opinions that do not
imply any false facts (ie. After reading the news story, I think the superintendant should resign; The superintendant is an idiot; Our school system deserves someone who can devote more time to school business; The investigations into his administration are troubling).
You can also state proveable truths (ie. the superintendant is under investigation according to the news story).
You can relate any true personal experiences, with no exaggeration or embellishment (ie. I saw him doing thus and so; I spoke with him and he said such and such).
By sticking to proveable facts and pure opinion and what you know for a fact from personal experience, you will not (or should not) lose any defamation suit.
In your neighbor example, yes, you could sue your neighbor for posting that you are a tax cheat, if you are not a tax cheat. It would be up to him to prove you are one. Defamation suits are not inexpensive claims to pursue, however.
There really should be solid evidence of reputational injury that can support an award of damages large enough to offset the costs of pursuing the action. It is, of course, a guessing game, because no one really knows what a jury will award in the way of damages (if they award anything at all). Although
economic losses generally do not have to be demonstrated in order to sue for defamation, being able to show an economic loss has been suffered as a result of the defamatory publication (ie. job loss, loss of promotion, loss of clients or customers) makes a suit more likely to be worth the time and expense that must be incurred.
Sometimes even suits that have merit will not be worth pursuing. It may not make financial sense to file a claim or, because a public record will be generated by the suit, it may not make sense to publicize even further any defamatory comments that were made, or the defendant may not have any money to pay a judgment or any assets that can be attached, making any damages awarded uncollectable.
Lawsuits are all about weighing the pros and cons, the benefits versus the costs.
One additional note: Public figures/officials must show that any defamatory statements published about them were published with "actual malice" (a deliberate intent to harm, through either prior knowledge that what is being published is false or with a reckless disregard for the truth or falsity of what is being published). Actual malice is a difficult "fault" element for a plaintiff to prove in a defamation suit.
The actual malice standard of fault allows for more freedom in discussing issues of public interest and concern, without fear of losing a defamation action. A superintendant, or the superintendant you have questions about, may very well be seen as a public figure/official in Pennsylvania. I haven't reviewed Pennsylvania case law to tell you if this is the case throughout Pennsylvania, however.
But, to answer your last question, yes. If you can back up whatever negative or defamatory things you may choose to say, with proof of the truth of your statements, you do not have to worry about losing a defamation suit (although you may still find yourself having to defend against one in court).