Yes, it is. Deeper has been designed for extensive outdoor use in a range of conditions and climates. It is ruggedized, so it is resistant to bumps and even pike attacks. Even so, please avoid physically damaging your Deeper - very strong impact can damage its internal electronics.
Deeper models are water resistant up to a depth of 1 meter (3.2 ft).
It will also work just fine in salt water, but it is advised to clean the device with salt-free water and then dry it off after every fishing session.