deny deletion of a file without omiting w permission

how to forbid deleting a file even though the file is owned by the user?

I thought of setfacl command on solaris. Any hints please?

thx

also you can see special bits in chmod.

The user could just change acl entries if (s)he owns the file. What you need to do is change the ownership of the directory where the file is to be some other user (root, maybe). And then change perms of the directory to something that is not writable by the user.