Any other Terminal / shell based options to strip all ACLs and extended attributes from a folder?

I'm having some trouble deleting some folders that contain nothing and have no processes or kexts utilizing them (lsof | grep path_element). When I try to delete them (as root) I get:

root@hostname /# rm -fr /path/to/folder
rm: /path/to/folder: Operation not permitted

Even after executing the following to strip ACLs / extended attributes, I still cannot rm -fr the folders:

sudo chmod -RN /path/to/folder
sudo xattr -c -r /path/to/folder

Executing ls shows no attributes:

ls -lea -@ /path/to/folder

Any other options to ensure all permissions are stripped and that an rm operation as root should work?

The culprit that was stopping the folder from being deleted was apparently flags being set and so the following finally allowed deletion:

sudo chflags -R nouchg,noschg /path/to/folder