If you get 'fresh' fuel from a high-turnover source there is little need even for stabilizers for long term stability; however a bit of stabilizer will retard fungal growth.
The probable most common 'contaminant' of 'diesel oil' is a fungus ("kerosene fungus" or a 'resin forming fungus') so simply open and inspect periodically for the build up of 'scum' on the jerry can walls. If you keep the 'caps' tight, you'll probably have no problem.

Contaminated fuel will be 'hazy' looking. Already contaminated fuel will begin to 'agglomerate' particles - bigger and bigger particles that 'grow' .... use an enzymatic stabilizer. ValvTect fuels (common on the S and SE coasts) usually have an enzymatic stabilizer already added.