A. Brown wrote:

Several years ago, my DH used marine spar varnish to coat the wooden
pillars and deck railing on our front porch. It's now peeling off the wood.

I'd like to refinish it (with something else!), but am unsure of how best
to remove the existing varnish.

Suggestions please?

Any mechanical device, sander, scraper, wire wheel, will risk damage to
the wood, and be difficult to fit into grooves and corners. I think the
best way to remove varnish is a chemical paint stripper. Get one that
cleans with water, and some scrub pads, a pile of rags, and a good pair
of rubber gloves. Put something on the floor to protect it from drops.
Follow the instructions closely.

An alternative might be to sand and put on a couple of coats of new
varnish; be sure to get UV protected varnish to minimize damage from the
sun, and just resolve yourself to refinishing every few years, which you
will have to do with almost any paint you use.