There are two common styles of banana plugs (not counting the various methods of wire attachment)...
One style is a tandem design
where the individual plug for each conductor is held apart from one another by use (generally) of a plastic substrate that prevents he two conductors from shorting - save it be placed upon a conductive surface that might provide a conductive bridge between the two conductors allowing a short from occurring.
The other style consists of the use of two separate plugs
, one for each conductor. These are not held apart from one another and when unplugged, they can, and often do make contact and short the signal from the amplifier.
If the later is the case, I might suggest either replacing them with the tandem model that avoids the issue, or I would cover the upper conductive portion of the plug (all but the actual insertable pin) with color coded shrink tubing. This will not prevent the pins from shorting as the tandem model does when not inserted into the speaker, thus requiring continued due diligence, but it will provide a modicum of additional protection while avoiding the problems with messy electrical tape.
Personally, I would simply opt for a pair of tandem banana plugs and minimize the risk of the conductors shorting.
Edit: for clarification, as some do not seem to realize this - the potential for shorting is NOT when they are properly plugged in to the speaker!
The threat is for when the individual plugs are NOT plugged into a speaker and the connectors then make contact and create a dead short to the amp!