Invest in a black light and a probe to detect uric acid crystals to identify where pets have pee-ed and where they may be marking their territory. 

I am not suggesting doing this for the roof but two ways to convert insoluble iron oxide( rust ) to a soluble form that is removed with a water rinse is to use either oxalic acid ( 5% solution on the rust for about 30 minutes( can wet towels so it adheres and does not run off) in water or a commercial product called "Iron Out" which is sodium hydrosulfide I think.

Consider having it etched - either acid or sand-blast - to change the appearance.If you MUST paint, please use some neutral color - nothing which stands out.

A combination HEPA/Acid gas may be more appropriate.

It appears to be a caustic soda or acid. 

we've tried 2 types of acid and pressurewashed...any good ol' boy tricks??

In finance and accounting we look at a "Quick Ratio" (also known as the Acid Test) this shows the ability of a company to meet obligations, but this only looks at current assets or liquid assets and current liabilities, real estate is not a liquid asset.So we move to other ratios like "Current Ratio" and "Cash Ratio" these to help to illustrate the ability of a company to cover current debts.As to mortgages or long term debt, coverage is difficult to predict due to uncertainty over longer periods, but by looking at the current coverage and cash available we can see what funds remain for these other obligations.Most everyone is familiar with the debt to income ratio we suffer through at a loan application, say 24/36, meaning that you should not pay more than 24% of your income to current liabilities, revolving accounts and car loans, the 36% includes the 24% to establish your ability to cover the mortgage, total debts should not exceed 36% in this instance.

What I have done....1 regular mopping with cleaner and bleach2 brush with acid wash3mop with the “microbe” ( I forget exactly what it is called) wash made for that.Use grout sealer when you’re done.

Salt Water corrodes a car like battery acid.

An acid product, and mechanical scraper, etc?