can I change unmount order when system is shutting down?

In fstab I have these strings:
none    /root/user_rw  tmpfs    rw,size=128M,uid=1001,gid=1001           0 0
none    /home/user     aufs     rw,dirs=/root/user_rw:/root/user_ro=ro   0 0
It unmount /root/user_rw first, but this directory used by aufs in /home/user. So /root/user_rw can be unmount only after /home/user.

I have error when shut down system: /root/user_rw is busy. How can I solve this problem?