Goodbye to the garish, inept horror story that is the Canon strap.
Here you can see what I am going on about – fancy being a walking billboard for Canon? Heck, I just paid them nearly $5k for the gear – if they want me to wear that, they need to pay me. Plus free repairs for when it slips off my shoulder. The Upstrap has a broad rubber pad with nipples on both sides. It is far more comfortable and simply does not slip. This is the SLR model for cameras over 2.25 lbs. I used to use the lighter RF/DC variant on my Leica M2 and M3.

Here you can see how it is threaded so that the ‘tail’ can be folded in between the two sides and retained by the slider. Neat.

Recommended without reservation unless, that is, you prefer gold chains displayed on your chest.
Here are the detailed instructions – there are many incorrect ways to install one of these and one correct one. Follow these instructions and the strap cannot become detached from your eyelets:

When threading the strap through triangular keepers be sure that its surface contacts one of the two non-opening sides, as the sharp ends of the latter can gradually wear through the strap material. Triangular split D-rings are far better than circular ones as you cannot prevent the opening area rubbing on the strap’s material with those.

You do not want the strap in contact with the arrowed side of the D-ring.