How to preserve home-made salad dressing, without using bad preservatives?
What is a "bad preservative"?

The main additive preservatives used today are ascorbic acid, citric acid, ethanol, salt, sodium nitrate (pink salt), sugar, and vinegar - all of which have been used for centuries, and other than with excessive use, are not seen as harmful

Weird chemical preservatives are often only used with weird chemical ingredients, stick to basics and you'll be fine

Pasteurisation, electrical pulse, and other heat treatments are used commercially and give products those amazing shelf live times. Without specific equipment and monitoring systems they are hard to reliable reproduce at home

Your home made dressing will last long enough in the fridge for you to get bored with it and want a new flavour :-)