how to stop outsided lights blowing?

You do not say how often the lamps blow or what type of lamps they are - no matter.

The life of a tungsten filament lamp depends on the quality of the filament - you may be unlucky and have a bad batch or you may be using bargain-basement lamps. Extended Life lamps can be bought.

Thermal shock from repeated switching on and off will shorten the life of a lamp - there may be an intermittent bad connection in the circuit.

Over voltage will cause a lamp to fail sooner - but it is very probably not a factor in your situation.

The connection style may or may not be kosher but the lamps will neither know nor care - they just need mains voltage to turn on and how it's wired to them is of no consequence.

Peccavi
July 2010