I use to catch them in the sping and I would keep one on a hibiscus plant next to a window. As long as you keep them well fed they usually won't stray. Spray the plant everyday so the mantis can drink the water drops off the plant leaves and that's about it.

They are very abundant in the feilds around where I grew up. The ones I caught were Chinese Mantids (Tenodera aridifolia sinensis). I use to catch a nice sized female and keep her well fed on moths, grasshoppers, crickets, & spiders. The females are the bigger of the two and can get 1/2 a foot long!
