That depends on the type of horses. Are you talking about riding horses, or work horses? Do you want to be near other people with horses, or does that not matter? Have you considered bording at one of the many stables around Austin and buying a home close by?
The land to the West of IH35 is very rocky, not always good for horses, but there are some old pastures that can serve very well. East of IH35 is old sea bed and there is a lot of topsoil in many places, much less rocky.
But just looking for horse property to rent could get you into a part of town that doesn't meet your other needs. If you have additional requirements, post them to this question, or check out my profile and see if my services might be a good fit.