How deep should I deep before laying pavers. I want a long lasting patio surface that doesn’t get easily damaged because of erosion or floods. I know that digging the base deep enough during installation can help prevent the pavers from shifting as well. However, I need to know just how ‘deep’ is deep enough.

If you go as deep as your frost ine to start the gravel base.. you will eliminate frost heaving which in itself can wreck your work over time....I'm sure you can get away with less than that however.

Most pavers are installed on a gravel/sand base. You would have to dig down about 6 inches plus the height of paver.

Chuck

I see the post is a bit old but for others to see visiting the site Im sure you know the basic layouts but this may help

Hears what we do on the jobsite in PA and goes from 100 to 0 degrees, plenty of rain, We dig as follows.
1. Brick finished height is 1” above cut grass then add rest of Paver thickness. .
2. From bottom of Paver ¾ to 1' for concrete sand.
3. From bottom of sand min 6”.. 2A modified stone (that's ½ to ¾ limestone with quarry dust mixed in)
4. From bottom of crushed stone Woven Cloth keeps weeds out

Dig out that depth and tamp dirt flat. Install woven geo cloth.
Rough spread crushed stone and mechanically tamp stone (to many home owners use a hand tamper and that's why many walks sink and move Carefully spread rest of crushed stone to its finish height tamp to finish height, this must be fairly accurate.

Now set your plastic spiked side rail widths. Use this for a guide to spread in the concrete sand. I use a 2by and notch it so the top edges go over and pass the plastic rails and the notched inside of the 2by comes within ¾ inch of crushed stone. This sets you concrete sand bed at perfect height. Be aware the plastic rails are to be 99% perfect in grade and the slopes required for runoff etc.

Note stone base has to be min 6” wider then borders edges so spikes grip and stay solid, stops border movement. After all this is done its time for the Polymeric sand and agin many screw this up and another reason pavers walk later .

http://www.techniseal.com/web/faq.php?surface=sand

Make sure the surface is VERY dry. Liberally apply polymeric sand and sweep at an angle until joints are full. Now use left over woven cloth doubled ( takes two people) and run mechanically plate tamper over brick while other fella pulls woven cloth in front so tamper doesn't chip Pavers. This set that sand tightly. Add more polymeric sand and agin sweep at angle and tamp. All instructions are on the polymeric sand bag wet as required. This gives you a VERY solid walk