I feel that the grid in any developed country is INHERENTLY and UNAVOIDABLY vulnerable.
TPTB may well have better defences against a cyber attack than we know about, but not against a simple physical attack.

Simple observation shows how vulnerable large grid substations are, they are too numerous to effectively guard. The equipment is almost always out in the open to facilitate cooling.
Enclosing the equipment in buildings is not only hugely costly, but adds its own risks including increased fire risk, and storm or earthquake damage to the building.
Anything out in the open is vulnerable to attack with weapons such as hand grenades, high powered rifles and small rockets or missiles of various types, or improvised bombs chucked over the fence. Terrorists have ready access to such items.
Most substations are not manned or guarded and a single armed guard would be ineffective against a group of terrorists.
No amount of armed guarding of the perimeter protects against high powered rifle fire or an anti-tank rocket fired from a rooftop a few hundred feet away.

An attack on a single substation would not be THAT serious, fires, blow ups and storm damage have after all occurred previously without any widespread serious consequences.

An attack on a significant number of substations and on long distance transmission lines could be very serious indeed.

IMHO, the government should subsidise the manufacture of spare transformers, switchgear, high voltage cable, and related equipment in order to facilitate prompt replacement of damaged equipment.
This spare stock could be stored in a military base or other secure facility.

Apart from that, not much can be done IMHO, resources should be concentrated on equipping all important buildings with backup generators, or proven design and regularly tested, together with ample fuel.
The government should also keep a supply of large and medium sized transportable generators, and a very large reserve of diesel fuel for emergency use. Also stored on a military base to protect against theft.