There's probably little need to define what "guarding" actually means. Even so, Merriam reminds us that, in it's verb state it means: to protect from danger especially by watchful attention : make secure.
I think we'd all agree that guarding is, most often, an intentional initiative. That places it squarely in the realm of defensive versus offensive tactics (think football) - though both may be necessary to ensure the safety of heart and tongue. Afterall, the scriptures have much to say about waging war, and about the wearing of armor when doing so (think 24/7). If protection and guarding weren't so vital, would we be instructed to armor up as we are (think Homeland Security)?
As I read through Old Geezer's post, I flashed back to a scripture that tells us a lot about what words actually mean, beyond the obvious need to communicate. They are the cascade from, or the overflow of what is rooted in our hearts (Luke 6:45, Matthew 12:34). What we say reveals a lot about who we are.
Above all else, guard your heart,
for everything you do flows from it.
There are a lot of people in my life who take great delight in telling it like it is, or who eagerly grab center stage. I'm one of them. I appreciate straight talk and candor; being direct and truth telling (think politics). Even so, I know I am guilty (and likely, so are they) of merely wanting to get my opinion out there.
There's just something about wanting to be heard (or having one's say) that is so tasty and tempting!
No wonder I am challenged by God's many, myriad, multiple, meaningful admonishings to guard the headwaters of thought and speech, the heart; and the mechansism for delivering its contents, the tongue.
Those who guard their mouths and
their tongues keep themselves from calamity.
Set a guard over my mouth, LORD;
keep watch over the door of my lips.
Do not let my heart be drawn to what is evil
so that I take part in wicked deeds ...
Those who guard their lips preserve their lives,
but those who speak rashly will come to ruin.
I can think of no better word-picture for guarding my heart (and the tongue that takes it's queue from it) than that of a lioness fiercely protecting her cubs. It is then that I understand more fully what is at stake (think marauding hyenas). It is then that I am better able to value the placement of boundaries, and to take courage in their being guarded (think Lion of Judah).
... in every situation, by prayer and petition,
present your requests to God.
And the peace of God,
which transcends all understanding,
will guard your hearts
(and the tongue that takes it's que from it)
and your minds in Christ Jesus.
... I know Whom I have believed,
and am convinced that He is able to guard
what I have entrusted to Him ...
2 Timothy 1:12