alternative for user immutable flag on ZFS

[Michael]

Hello,

I have some important files in my home directory and I want to make sure 
that they are not changed/removed by my mistake.

So I'm looking for something that prevents all programs (like rm) from 
changing these files even if I tell them to do so. But then on some rare 
occasions I really need to modify them so there must be a way of 
clearing these restrictions. And all that from my user account without 
root privileges.

Normally I would set user immutable flag, which can be manually cleared 
in case when I know what I'm doing. The problem is that I can't get them 
to work on ZFS and it looks that it's not supported.

Are there any alternatives or different ways to achieve my goal? I'm 
using FreeBSD 8.2-Release.