Use lumenaddr to generate a Stellar address with a custom suffix. Download the source code, run the program offline, and copy down your new secret key.
Visit the lumenaddr site and click the link to the Bitbucket repository:
Visit the Downloads tab on the Bitbucket repository page, download the zipped repository, and unzip it.
Input your desired suffix into the text box and click generate. Go walk your pet porg while you wait; four letter suffixes can take up to two hours to generate.
Quit your browser. May sure your secret key is not saved in your computer's copy and paste feature. You can reconnect to the internet now.