I don't think it's as simple as laying down a bunch of rules, and expecting people to toe the line or be fired. You'll never get a dedicated, motivated workforce that way. You will just become the big rectum that everyone hates rather than respects.
Don't get me wrong. It is critical to establish standards and hold the employees accountable to them. It is also critical to do everything you legally and ethically can do to reform or eliminate the ringleaders. That side has been covered.
However, communication and reform is a two way street. There are reasons why these people are not motivated. Have sessions with the employees where THEY do the talking, airing their issues and concerns, what they think and feel. You said many of these people have 10-15 years. They have things they can contribute if you remain open to them. Now, let's be honest and make it clear that you can't necessarily fix everything to their liking, but making even a couple of minor changes in response to their input adds to thier value, and therefore their motivation.
