If you want to keep the union out of your business:
1) Treat your employees like partners not peons. Your employees are not an expense, but your most valuable asset. They need to know that you feel that way.
2) Prove it! Provide excellent wages, benefits, profit participation, and merit based bonuses to ALL employees, not just the select few.
3) Provide ongoing training and clear career paths to engage your employees. Develop loyalty, low turnover, low absentee rates, and high productivity by being loyal to your employees. If you are enrolled in their success, they will be enrolled in yours.
4) Ask your employees for their input. middle management needs to be in relationship with the workers so that when upper management wants a result, the middle manager can ask the employees what they need to create that result.
Only respect, communication, and inclusion will keep your shop union free.
If you can't do those things, then someone like me will show up with organizing cards and help you do the right thing through collective bargaining.