How can I overcome the causes of anger? When I get angry with someone, I can usually calm this feeling after some time through meditation practices.

But I'm wondering how can I overcome the causes of this 'anger' in a way that I don't get angry anymore with something?
Excellent that you are interested in this! You are motivated to attain Arhatship! Permanent uprooting of the poisons is achievement of Theravedin Enlightenment/Arhatship.

I will summarize the pathway in a recursive way that you can not only use for any of the three poisons (anger, greed, delusion)... but you will find will be permanently valuable for the entire path!


1st training: restrain your action by following the Eightfold path. Force yourself to follow Right Speech, Right Action, Right Livelihood no matter what!
2nd training: use anything you would use for the 2nd training, concentration. This can be a contemplation that fixates your attention away from the anger (breathing, brahmavihara, etc.)
3rd training: vipassana. Be clearly nakedly aware of the emotion as a sensation. It will dissolve.


The 3rd training is hard to do without proper advancement in 2nd training.
The 2nd training is hard to do without proper advancement in the 1st training.

The 1st training you must do or else you will sink into a lower form of existence in the next life.

Rmemember that the above method may seem like a lot in words but it's main success is in the lifestyle path you choose (animal-killers or prostitutes are not Right Livelihood and will experience more poisons than others always) and being mindful in the moment (#2 and #3), transforming the emotion. This can be a matter of a split second.

I have not referenced any lengthy suttas in this text but these are all true things said by the Buddha. I would recommend seeing the chapter on the Three Trainings within the free book Mastering the Core Teachings of the Buddha for more info and read the entire book.
Super big secrets.