In short, as long as you can stay 50 ft. or more away from a Diclonius, they should be easy to dispatch with the aforementioned methods. They are highly vulnerable to being attacked from a distance with large firearms and explosive ordinance.

In Elfen Lied they weren't attacked as aggressively because they were supposed to be a secret and Lucy/Nyu was often in a urban area where you can't really utilize that much firepower without bringing a lot of unwanted attention and possibly civilian casualties. If they were more open and public about it, we'd have probably seen quite a few of them get blasted to bloody chunks with Anti-Tank Rockets and the 30mm M230 autocannon of the AH-64D Apache Attack Helicopter.

The answer in that situation really is more Dakka.

• >MFW I'm ready for June.

When you think about it, Diclonius are really easy to kill as long as they're not Lucy/Nyu going nuts in the last few chapters with the giant planet destroying Vectors.

Really all you would need to do is stock up on Anti-Material Rifles chambered for .50 BMG or larger and other weapons of similar velocity as there is a maximum to what they can deflect. Chemical, Explosive and Incendiary weapons and would also be preferable as they will most likely not have access to HAZMAT gear or flame retardant clothes. Relocating to a less densely populated area would also be preferable so as to reduce the chance of having to deal with multiple Diclonius at once.