I have several solid stone pillars (approx 4' high) running along the edge of my patio. I would like to hang string lights along the stones using something like Q-Hanger hooks. But I do not know how to go about securing these hooks into the stone itself. I see online some plastic anchors that look like the kind that I would use in drywall but I'm not sure if that is the best option or if those anchors would work with the hooks I have planned.
Any advice would be appreciated.
I would only drill that stone as an absolute last resort. That not only damages it in an unrecoverable way but opens it up to faster degradation from weather, especially if you're in a frost zone.
Get some aluminum wire for bonsai (example). It's anodized in a suitable color and very easy to work with. You could also use coated steel gardening wire (per Tonny's comment) or even coated copper electrical wire. Wrap it around the stone and twist it at the light location, then use the tails to attach the lighting. As Criggie suggests in a comment, you could use a wiring strategy similar to how sparkling wine bottle caps are done:
You could also use decorative metal strapping (examples). Wrap it around the post, folding at corners, and use a bolt to cinch it on the outside corner. If you leave a gap between the straps you could attach S-hooks or similar to the bolt shank.
Whatever route you choose, protect the wire well from chafing to prevent damage and shorts. (Thanks, Chloe.)
There are many plastic concrete anchors you can use for this. The one I like best it the one pictured below. They come in a variety of sizes and will match the screw hooks you'd like to use. Your hooks are stainless steel so they'll last a long time and so will the anchors. You'd need a masonry drill bit to drill the hole but many packages of these anchors include the bit. Good luck
Personally I wouldn't drill it. I'd get some adhesive hooks, then throw away the adhesive part and use construction adhesive instead. That should be plenty strong to hold some outdoor string lights.
[Updated, since the target is the tall stone pillars, not the stone wall]
I would be reluctant to drill into the stone, not least because it may open the way to water penetration and frost-shattering. With pillars that tall it could be downright dangerous if they got frost-shattered and then broke. It may also be very hard work.
So look to methods that don't damage the stone and are reasonably inconspicuous. String or non-ferrous wire around the pillars (string can be dyed, unvarnished brass tarnishes to a brown that may be similar to the stone). Or, what I think I'd do, is to epoxy-glue some small cable tie bases to the stone.
After reading the given answers (as now), let me add mine :
If you plan to draw long lines for hanging your lights between pillars, the following is for you, else @isherwood answer should be the good way.
As a father, I always think about "where will this dam' child find a way to hang/climb ?". So, in order to let my daughter climb everywhere without risking some installation to fall, i tend to build really solid things.
Long lines will pull on the stone (traction force). You need to convert this into compression in order to avoid the rock to split.
This is achievable e.g. by adding a steel stripe (section e.g. 30x8mm) in the back of your stone, with a steel strapping.
These stripes must be strongly tightened to the ground and reaching the back of the strapping, facing the traction point.
By doing this, the bending on the steel will try to "crush" the stone pillar, thus creating a compression force instead of a traction one.
I Hope i did explain that in an understandable way.
Assuming the below-ground portions of these stone pillars are in pretty solidly:
Get a rough piece of rope (e.g. manila rope, not something slippery) and tie a clove hitch or similar knot around the top of the post. With the ends of rope coming off the clove hitch, you can either make them short tie up the lights right there, or make them long and have them reach to the next post and the next one and the next one, as a support line for the light strings. You can wrap the light strings around the support rope.
There are plenty of additional details and photographs about how to do this in various places online. Without copying in copyrighted materials, I'll link you to this article discussing the knot in a filmmaking and lighting context, and this one in a Scouting context.
