Lock Account field after time logged

[Yuki]

I want to lock Account field once someone logged some time on this issue. I tried behaviour and JJupin. I can make a field readonly by Behaviour but I can't catch the worklog event. I can use SIL listener to catch the worklog event and I can't disable a field by using IfDisable(). I don't know the reason. I tried the other fields and they don't work as well.

lfDisable("s2id_customfield_10101");