You will discover how much fun it is attempting to adequately insulate the can.

Why would it be any harder than a fence?

My thoughts would be forgetting to turn the fencer off before feeding the cats some time.

 

A canhas a much greater surface area and thus more capacitance to everything surrounding. So you will be dealing with charging a capacitor. I may have overstated the difference.

 

For your possible interest, below is a simple line-powered, capacitive discharge, electric fence controller (discussion here).
It has a 5kV, 0.5 Joule output pulse, operates directly from AC, and requires no AC isolation transformer, with isolation provided by a dual-output ignition coil.

 

First ever post so here goes.......

WRT the air gap technique, it's an old idea.
Being an early Wankel engined car owner (NSU Ro80), and it being a two stroke engine that consumes the engine oil (total loss system) to lubricate the combustion chambers, spark plug fouling in traffic can be a problem. Modern Wankels (and two strokes) use fancy oils (and less of it), so don't suffer the problem. To help with this, that nice chap Robert BOSCH designed some 'traffic' spark plug caps in the 1970s for the engine (listed in the manufacturer's parts catalogue) that have specifically what you are talking about at the start of the thread. Namely an air 'gap' within the plug cap.
I did a bit of Googling and came up with an abstract to a 1992 paper that re-visits this idea in relation to spark plug fouling (see link).
https://saemobilus.sae.org/content/922093/
I'm not prepared to pay the $33 US dollars to get this paper, but some enterprising young forum member may be able to find the full text out there on the interweb.

 

Adding a second spark gap provides a much faster rise time, but less actual energy. It adds no energy at all.