how to prevent edit custom field, which I have added my own?

[Nic Brough -Adaptavist-]

For a standard custom field, simply remove it from the "edit" screen.

I don't want to talk about other variations on this without a bit more information on what you're trying to achieve (telling you to do it in Behaviours when you actually would benefit from doing it in workflow would be a bit of a waste, etc)