No leaks guaranteed can be had simply by wicking it right, one wick tail over each juice hole and the very end of the wick tails overlapping between the juice holes but not overlapping over the juice holes themselves, poking them down into the holes in all actuality would just make wicking less efficient and lead to a possibility of dry hits during chain vaping. Another good idea is to trim the wicks from the side reducing their volume, in larger diameter coils this is basically essential for efficient wicking.
People really just don't understand how to properly fill it from the top, since there's around 2mls that pools in the bottom of the tank that isn't even visible through the glass section, when you unthread the top cap, depending on what the airflow/juice flow control setting is, it could disturb the vacuum which will cause a push of excess juice up through the holes of the deck and cause leaking. The best way to avoid this is to flip the tank upside down, wait for the excess hidden juice in the bottom to drain from around the deck, close afc/jfc completely, then open it just barely to take off some of the pressure, then fill. You won't get 100% capacity doing this, but it's leak free. The only way to get 100% capacity (to where there's not even so much as an air pocket in the tank) and avoid ANY leaking is to bottom fill.
For some reason the knowledge of how RTA's and RDTA's wick seems to be lost on the masses, juice doesn't just flow upward because that's how you need it to, a vacuum pushing the juice up is how the wicking in RTA's and RDTA's works, it's also usually the same thing causing them to leak.