We are very lucky that although we only have the normal lap panel, 6ft, all along the back border of our property behind that panel fence is also a prickly hedge plus scrubby bramble - we had a scout down the footpath to see how penetrable our back entrance is.... and its definitely harder to gain access than many others along the route. The fence itself is 6ft but there's a 3 ft drop as well so effectively a 9ft barrier. Good advice about securing the panels so they cant be lifted though, and I would really like to replace the panels with something more solid and substantial.
One thing that isn't liked by those who climb over fences is a foot of trellis, not overly strong stuff as it needs to be able to break and cause a bit of noise when climbed on.
Another thing to remember is to bring EVERTHING of any use into the house in a lock-down situation. You wouldn't want to witness your shed being emptied in the middle of the night. They could use those bits of wood/bbq accessories etc. to start a fire and use your tools and your ladder to help gain access to your house, then ride off on YOUR bike! I think I'd leave some useless stuff out for easy nicking like the lawn mower. I'd also remove any large rocks from the garden. I think if at some point you had no choice but to bug-out quickly, you would want that carefully packed bug-out bag and a plan for all the family to meet at a 'safe' location should they get split up. That would be a reason to prepare a bug-out bag even though you plan to bug-in