Hens will happily eat all your slugs, bleach will kill your plants instead.
Soap is used sometimes to get rid of some plagues (because many plages use wax to avoid dessication or deter predators and soap distroys this upper layer) but remains in the soil aren't good at long term. Of course you can't use any common insecticide, because spider mites aren't insects, but you can use (or support) mite predators that will munch on spider mites.
Spider mites hate the moisture and, if is in a pot, just spraying water repeatedly can help a lot, or even solve the problem.
In a non sprayed garden with enough access to water and welcomed predators, spider mites aren't so much trouble.
This raises a curious question for me. My grandfather is from Ireland (Meaford, Canada now) and still an avid gardener. He swears by Murphy's Oil Soap (diluted, 2-4%) to deal with harmful insects like Spider Mites.
Does anybody have any more scientific insight on that? Mind, he uses it on a far smaller scale, mainly spraying his flowers, vegetables, and other garden plants with a small spray bottle. Not much of a lawn guy.