You can use third party defragmentation tools that have central management consoles to manage the tools, monitor systems and report on fragmentation levels. These tools have the ability to start defragmentation based on a schedule or a fragmentation threshold level (tool dependent). What they also do well is provide reporting on how things are going on the systems you monitor fragmentation wise.
Here is a comparison page for some of the major defragmentation applications:
Comparison of defragmentation software
The big three from when I did some research several years ago:
Keep in mind that Windows includes basic defragmentation. You can schedule this using TaskSchedule. Basic defragmentation does not defragment page files, hyberfiles and the like. There are some other free tools available that can do various items like page files. This all requires you to piece together and and devise your own monitoring. If you need reporting and monitoring purchasing it is always simpler.
If you can justify the cost of a managed defragmentation program, these will all do a good job. Test each to see how they impact system performance in your environment while defragmenting as well as their management and reporting capabilities.
First, don’t wait for your hard disk drive to be hardly used before defragging it. You have to maintain a certain defragmentation period as part of the computer hardware maintenance for your computer system.