You can bring them in on your clothes and shoes... say you walked by a bush and brushed your pant leg against it... it jumps off in your room...
houseplants... prbly indoor outdoor pets..
Then, you know, bringing in clones.
It's a pain in the ass, but, if you can do your garden work in clothes that you have not worn outside it really helps.
I do it nearly every visit.. haven't had spider mites indoors in a very very long time. At least don't do your work in clothes that you have spent a bit of time outdoors in..
like say... after cleaning up your yard, taking a hike, walking the dog... don't go straight to your room in those clothes.