I wrote about this before, but its important enough to write twice

How to revoke write permissions to a directory

How to revoke your own user permissions 

$ chmod u-w dirname

How to delete all permissions from anyone on your system 

$ chmod a-w dirname

removing write access on a file does not stop it from being removed,

you must remove write access to the directory to protect the file from deletion – Ice Bear

How to test this

To test this, simple change the permissions and try to $ rm any_file_name. You can even rmdir dirnameand it will protect the directory from deletion