Borax will kill shit... it's natural... but it's harmful to plants and animals. I've heard that some people mix it with honey or sugar water to attract bugs to their deaths(like ants). Keep it away from plants & pets ... it's far worse than salting soil. The oils probably won't harm anything when sufficiently diluted. They'll mainly serve to annoy pests, and they can help cover smell.
You could also try companion plants. Many flowers, herbs, ground cover, etc will deter certain pests. They don't require much light, you can also plant stuff solely to battle smell.
If not the actual plant or herb, usually getting an extract of it will serve the same purpose for fighting pests. You can mix several oils together, shake it up with water, spray it quick. Always shake it up before use. Don't mix more than you plan to use.. with water.. Use alcohol if you plan to store it in solution for longer(you could make a 10 to 1 alcohol solution and then do a 10 to 1 with water). Most health food stores sell small vials of essential oils, as they're called, these are typically 99% pure. You can dilute them 10 to 100 to 1 with water or alcohol. Also, store them in a cool, dry, dark place sealed tight!
Unless you have a specific pest problem just try citrus/mint/tea tree oil. I like these particular smells(and they're not overly expensive), you may like others. Do a little Google/shopping. Some could probably attract pests.
