So with the multitasking feature inside (iOS > 4), you need to force to really quit the application.
For that, use the Multitasking bar to close any app you want.
- Double tap the Home button to bring up the Multitasking bar
- Press and hold anywhere on the multitasking bar until the icons on it start to wiggle.
- While they are wiggling, each icon has a Minus sign symbol above it.
- Press the Minus symbol above Marine US application to close it down.