Hi Ian,
One key thing to do is never remove the tyre completely from the rim until you have located the puncture hole in the tube. ie leave one bead on the rim and do not rotate the tube when you remove it from the tyre - keep it parallel with the wheel and pump it up so you can find the hole by feeling the air rush on your cheek or lips or in water, mark the hole on the tube with a piece of chalk or marker pen and offer the tube up next to the tyre so the valve is next to the valve hole and the tube is still in the same orientation as it was in the wheel at puncture time, this way the chalk mark will line up with the offending item in the tyre or the bad bit of rim/spoke head. Now finding the thorn is easy but remember to remove all. there may be more than one .
Next when you have repaired the tube or when you put a new tube in do not use any tools except your thumbs . As you fit the tube keep checking that the rim tape stays in place and the tube is not being nipped by the tyre by peering down inside the rim .
As you inflate the tyre check it stays concentric with the rim - there is a fine line visible just above the rim on the side of the tyre to help with this.
Land Cruiser are not as puncture proof (Very thin between the raised tread profile) as Marathon or better still Marathon Plus Smartguard.
Lastly, if you are still awake, check your tyres regularly for anything on its way in, you won't always get a puncture at the first revolution but sometimes after repeated miles of hammering the thorn through.
Or ( this will appeal to the paranoid) have you upset someone at your place of work/college whatever- I repair other peoples punctures for a living and sabotage is rare but not unknown, even down to removing valve cores......
best wishes and good luck...