An armoured vehicle would not help with the type of IED's used. Even an APC would have given little defense...unless it was a Casper.
My two cents worth on improvements ( and I am not saying none of these are currently in place with SA companies ) would be;
Move to the Dyncorp side of the airfield.
Move into the green village. You could use the back gate.
Move to Bagram.
Move to Khandahar.
Use local sedan transport. Split large groups.
Vary routes. Yes, there are only two...
Defensive driver training.
No travel in uniforms.
Spotter vehicles.
Ensure the drivers are not based at the compound and know little of the crew life within the compound.
Split the compound into smaller groups and at separate locations.
Heavy duty gates and mantrap areas.
Have razor wire / electric fences along all rear walls.
Use perimeter motion detection.
Panic siren and panic buttons accessible at all locations.
Safe areas secured with blast doors and armed security based within the secure area such as a roof.
Have access control to intermediate areas, especially entertainment / dinning where large groups gather at set times.
Employ a security manager who is separate to the business unit and can make independent calls.
Dis-associate yourself from the principle client and actively advertise that.
Screen local staff.
Adhere to all security advisories issued by the private security companies.
What is worrying is this seems like a planned and co-ordinated attack. I.E. this was not being at the wrong place at the wrong time. In other words, assume the worst and consider the compound to be the next target.
This now makes most of the civilian contractor compounds unsuitable. It is time to move asap.
Oh, and like when the weather is marginal, refuse to fly. If it's meant to be a black day.....it's black and cancel flights...
Please let lessons be learnt and practical solutions be implemented for those that decide to stay. As South Africans, we have become to desensitised to violence and in turn have become complacent.
For the rest, lets see the local aviation community in SA offer work to those guys who have young families and choose not to return.
Come on SAA, how about offering the contract guys a slot ?