EKORRE Ceiling Hooks from IKEA, at only $3/pair, have been my go to anchor for securing shade sails around my back yard (along with many other things as well). They were originally sold with a children's line of furniture and toys that hung from the ceiling or beneath bunk-beds and these were the ceiling hooks supplied with those products and they were also sold separately.

While it seems as though they are not available at IKEA stores anymore, they are available through several other retailers.

Supplies

EKORRE Anchors
Shade Sails (Coolaroo brand are the best)
1/4" Lead Masonry Anchors (Masonry Application)
1/4" or 3/16" Lag Bolts (Wood Application)

Tools:

Drill (Preferably Hammer Drill)
1/4" Masonry Drill Bit
Other Size Bits as Required for Wood Application
Hammer

Step 1: Mounting the EKORRE Anchors

The EKORRE anchors come with 4 pre-drilled holes that are the perfect fit for 1/4" lead masonry anchors (left image above).

For Masonry Applications:

Position the EKORRE anchor, while paying attention to how you want the hook oriented, and mark the four holes
Using a 1/4" masonry drill bit, pick one of the four marked holes and drill just that one hole (don't worry if the drill bit "walks" a bit and you miss the intended mark slightly.)
Reread step 2, drill ONLY ONE HOLE!
Using a compressor, air bulb, can of air, or your own hot air, clean out the hole from the masonry dust. (Flushing with water is even better.)
Position the EKORRE anchor back over the holes, insert one lead anchor through the EKORRE and into the hole you just drilled. Ensure the EKORRE is flush to the wall and the lead portion of the anchor's head is fully seated then hammer the nail until its flush to the lead portion's head. (The nail penetrates the lead portion expanding it and forcing it outwards in the hole making for a secure and permanent hold.)
Adjust the rotational position of the EKORRE if needed by lightly hammering one edge of the hook
Using the masonry drill bit again, drill a second hole (I usually choose the opposite side hole, but it really doesn't matter). This time you will be drilling through the hole in the EKORRE and also into the masonry wall. (This serves to ensure the hole is properly located.)
Repeat step 4
Install a second lead anchor per step 5
Repeat step 7-9 for the remaining two holes

For Wood Applications, follow the same steps above with the following deviations:

Choose a lag bolt that will just fit through the EKORRE holes. (I think a 1/4" lag bolt actually is larger than .250" where the thread is, so maybe a 3/16" is the correct size. I'm not sure as I've only ever used these in masonry.)
Pre-drill size should be 3/16" MAX and may not need to be pre-drilled at all. It all depends on the type and condition of the wood.
Pre-drilling all four holes at once can be done as it is less likely for the holes to shift

NOTE: The exact size of the holes in the EKORRE anchors is 0.275".

Step 2: Strong Enough?

Picture above is the top anchor point for an extra large 18 foot square shade sail that covers an entire corner of the back yard. When it rains it gets weighed down by the weight of the water to the tune of 106 additional pounds (yes I calculated that.)

Only the force of a Microburst a few years back was enough to take the sail down, and it accomplished that by pulling our block wall down. The EKORRE anchor was still firmly in place (in a block under the rubble). So, yes, they are strong enough.

Step 3: Weather Resistant?

All of mine have been installed for over 10 years with no signs of corrosion, deterioration, or loosening over time.

Step 4: Finished

My purpose of this Instructable was to focus on the anchors and as such I didn't explain anything related to actually installing shade sails. However, I have plenty of experience doing so, and would be happy to help anyone interested as it is actually a bit more complicated than you'd think. But as with most things, pre-planning, and measuring many many many times are the keys.

Thanks for taking the time to read through my Instructable. Please send me any questions or comments you might have. I try to answer them all. Stay safe and healthy! Enjoy the Outdoors!