The ": ... ; " is a good start, but you can also put in the $ or # before the semicolon using bash's "\$". This makes it especially protective if you copy+paste+oops as root ;-)
You have to have a space after the ":", so ": ", but you can colorize that bit in modern shells so they have a use. I color them green or red depending on the exit status of the prior command (using the PROMPT_COMMAND bash var). I also leave out the space after ";" and just colorize it to be invisible, but that's a personal quirk.
More importantly, you can use the PROMPT_COMMAND to filter out braindamage as you build the prompt, and thus prevent filenames - which can contain ">" - or something from producing a redirect in your PS1.