If you think the case looks a little bulky, the website pointed out that the cartridge can actually double as a kickstand for your phone.
A Spraytect case retails for $39.95.
Both cases are available for iPhone 4 and iPhone 4s.
Another option is the Coyote Case. Designed for the iPhone with an Android case in the works, the Coyote Case emits a 110dB alarm and sends your GPS coordinates to your emergency contacts with a trigger switch and a tight squeeze.