Create a persistence file

Download the 1-GB persistence file and uncompress it your 1st hard drive(i.e. /dev/sda1).

Add the persistence boot entry

1. Extract the ISO to a working directory.
2. Add the following boot entry text in /path-to-your-working-directory/isolinux/live.cfg:

label DebianDog Wheezy live-boot-3x (sda1) 
root=(hd0,0) 
kernel /live/vmlinuz1 boot=live config persistence swapon rw-basemount quickreboot noeject autologin 
initrd /live/initrd.img

Recreate the ISO with the new boot entry

Replace /path-to-new-iso.iso and /path-to-your-working-directory/ of the following command and run it to create a new ISO.

genisoimage  -r -V "cust-debdog-iso" -cache-inodes -J -l -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o /path-to-new-iso.iso /path-to-your-working-directory/

Usage

On boot, select DebianDog Wheezy live-boot-3x (sda1). All your changes will automatically be saved in /lib/live/mount/persistence/sda1/persistence(i.e. /dev/sda1).

References

http://murga-linux.com/puppy/viewtopic.php?p=774457#774457