What is the best way to check a head gasket?

The test the garage did was testing for fumes in the water system, I have found this very unrealiabe in the past, I was told that there was no problem when in fact the head gasket had a leak and cost me a new head (very expensive).
2 Things to look for:
1. Oil in the water, this will make the water in the cooling system change colour, it will go a brown sludge colour.
2. Water in the oil, if you take the oil filler cap off then there will be a light brown sludge in the top of the cap.

Also if the water in the cooling system is being forced out of the pressure cap this is also a sign of a blown head gasket as the pressuer inside the engine increases.

Andy.
May 2005