Hiya Suspect,
Burn-off will always happen, but the better you get at sliding the less you will encounter.
It's a fact that far more often than we like to believe the slide never reaches the stopper...especially when fishing off flat beaches. On deep water points the gradient down to the stopper does provide additional assistance.
To prevent a burn-off these are the areas that count the most...
You must shake that bait down till you feel your arms may drop off...and then shake some more. Try different rod stroke patterns over the entire time that you are busy. I combine a number of different stroke actions from short quick stabs to long slow strokes through a 90 degree action.
Once your arms have fallen off and the rod is either in you hands or pension pipe matching the reels drag setting to the sea currents is VITAL. Here two factors play a role.
The first is that heavy grab sinker at the end of your line! Remember how hard you have to pull on your setup to get that sinker loose? Well thats just as hard as the running fish has to pull...except here the benefit of 100m of nylon stretch does not allow that 'shock relief'.
The second factor is the current in the water acting out on thick 0.50 - 0.55 mono. Currents will always cause a bow in the line and if you have not managed to get your slide all the way down the slide will sit in this bow and in some cases move up the line and into the bow...a slide CAN move backwards.
Now back to drag setting...a shark will not always swim away from you? It's prob accurate to say they hardly ever do maybe 1/10 times this can happen. The other 9/10 times they can head off in any direction. If there is a strong wash you can bet your bottom dollar that they will take full advantage of the moving water before or once hooked.
Thinking back to your firmly wedged sinker, a slide bait 5m from your leader, washing current and a slight bow in your line and a fish that decides to take off at a 45 degree run to the beach. Add a to loose drag setting to the mix and all that will happen is that your sinker remains where it was, your bow is made larger by the line coming off the reel and the chances for a burn-off greater.
I get around these conditions by keeping a tight drag which helps direct the fish back in the direction of the sinker. I may lift the rod, but only strike and set the hooks once I can feel the sinker has lifted and the dead weight of the fish is against the stopper.
If I get a few burn off's in a row then I drop the connection between the sinker and stopper ring as light as possible...0.40 at times. Would rather loose a sinker that a slide rig and FISH!
You have to combine simple logic and a small change here or there...or a combination of some of the factors I have mentioned to reduce your burn off count.
Please chaps...don't set your drags tight and then wonder off or catch a zizzz only to find a broken rod butt in the stand or drag marks to the beach indicating the last direction of your rod into the drink.
My last advice is try to imagine what's happening under the water...what factors are playing out and then act accordingly or different to prevent burn offs from happening.