Use Access Control List
To block the user 'user_to_block':
setfacl -m u:user_to_block:000 <path_to_directory_you_want_to_block_access>
m-> Modify file system
u -> user (this can also be a 'g' for group ACLs)
:000 -> Permissions in Linux filesystem (alternatively can be an octal digit from 0 to 7 or letters - read (r), write (w), execute (x))
You can check ACL with the command:
getfacl <file_or_dir_you_want_to_check_ACLS>
To remove ACL for one user/group(e.g., user 'user_to_block'):
setfacl -x u:user_to_block <file_or_directory>
To remove entire ACL (all groups and users already set ACLs):
setfacl –b <file_or_directory>
References
Another options and information can be found in man pages for setfacl
command:
man setfacl
Online Resource: http://linux.die.net/man/1/getfacl