Not sure if you specifically mean precautions relating to the patio door but you can buy locks which prevent the frame being lifted off the tracks, see extract from http://www.navanlockandkey.net/advice.html:
[FONT=Verdana, Arial, Helvetica, sans-serif]Patio doors are especially vulnerable to break-ins, so additional security locks should be fitted at the top and bottom to stop the frame being lifted off the tracks, and ensure that the sliding section is always on the inside.
A multi-lock system is recommended with mortice security bolts with removable keys at the top and bottom of both doors, and locks that prevent the doors from being lifted out of their runners. In addition to a multi-lock you should consider installing further security devices such as a burglar alarm or security lighting for overall protection.
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[FONT=Verdana, Arial, Helvetica, sans-serif]Remember, quality locks and bolts are only as strong as the door and the frame to which they are fitted. Check that the frame is well fixed, and if the woodwork is weak or rotten make sure you replace it.[/FONT]
about 2 weeks ago i bought deadbolts for a patio door in a lock shop in Capel St. now im sure you can get them elsewhere, they were made by Chubb, a bit expensive at €33 each, i thought but easy enough to fit though