What can an Indiana employer do about hiring an Employee who might have trade secrets?

Other than not hiring a person from a competitor because you know they have trade secrets, I find the following general rules from Trade Secret Misappropriation By Employee: Is The Employer Liable? are a very good start:

...., employers hiring employees from competitors should, at a minimum, first ascertain that there is no non-compete agreement with the prior employer. Second, the new employer should have the new employee sign a statement for the personnel file that the new employee either does not have knowledge of any trade secrets of the prior employer or shall not use any such trade secrets of the prior employer while employed by the new employer. While such a statement may not necessarily assure protection against liability, it will at least show a good faith attempt to avoid misappropriation of trade secrets.

Employers should ask if there is a non-compete agreement of every employee. Without knowing any particular positions or employee's talents, the employer should consider placing the employee in a position differing from their former job.