A property with six buildings and four hundred metres of boundary cannot be secured uniformly, and trying to do so produces an expensive, evenly mediocre result. The useful approach is triage: identify the two or three points where somebody would actually come in, spend properly there, and accept that a garden store at the far corner does not warrant the same hardware as the door to the main house.
In practice the priority list on these properties is remarkably consistent. First, the quiet section of perimeter and whatever gate sits on it. Second, the building furthest from the house, because it is unobserved and often contains tools that make everything else easier. Third, the door between the garage or garden area and the house itself, which is frequently the weakest link in an otherwise well-defended envelope.
The other thing scale demands is a coherent access structure. Where a household, a staff family, a gardener and a pool service all legitimately move around one property, an ad-hoc pile of keys becomes unmanageable and, eventually, uncontrollable. Designing that properly is master key system work at estate scale, and it is what makes a departure or a contractor finishing a clean, single event rather than a vague worry.