Multiple Alternator Replacements

All of the check lights went on with the car (check engine light, battery light, all of them), and the car was driving strangely. I had the alternator checked, and it was bad, but the battery was good. I replaced the alternator, but didn't tighten down the battery clamps very well after replacing the alternator. The replacement alternator went bad and the battery went bad. I replaced the battery and securely tightened the battery down with the clamps, and put in another alternator, but the battery light comes on and off intermittently while driving. I had it checked and the alternator is bad again. I checked the fuses to see if any of them were visibly bad, especially the fuses that pertain to the alternator. I checked cables to see if I could find any issues there, but the cables and fuses all look ok. I haven't tested fuses with a multimeter yet. What could be causing the alternator go keep going bad?