I recently had a minor termite attack on my front porch, and the termite guy
came out and said all I needed was to repair the damage and have the front
porch area treated. He injected poison under the porch. It seemed to have an
effect because a few days later, earth worms started crawling out of the crack
between the porch and foundation.

I plan to seal the crack with some silicone sealant, I assume this will help
prevent termites crawling up through this crack again???

that was a few months ago. Recently I was working on a couple of wooden
vegatable garden boxes (about 6' x 10' in size, 1.5' tall), and I found some
termites living in the wood. I used some over-the-counter termite poison to
treat the areas where I saw termites, they seemed to die quickly when contacted
by the poison, but I assume there are still more living under the ground there.
I also have a few fence posts that are rotted under the ground, maybe sign of
more termites.

My question is, should I be concerned that my property is infested with
termites and have the whole perimeter of the house and fence treated? Or is
it normal for old wood sitting around like these vegetable garden boxes to have
occasional termites? The pest guy said that other than my front porch, the
house is well designed and termites are unlikely to find their way into the
house, especially if i keep an eye for termite evidence and have him come out
every couple of years to take a look.

Any thoughts?
Thanks,
Paul