This is something I'm asked regularly and the advice is always the same. Use a stop bead to add to the strength of the edge but make sure you bed it well into a good and continuous line of render or adhesive mortar. This will create the seal you need at the edge and give you a perfect finish.
Be careful, if you opt for the sealant technique as when it goes on, the sealing bead you create can be of different thicknesses as you run it from brick/block/stone to mortar and so not behave entirely consistently over the life of the render. It can also increase the risk of an air pocket being trapped between the sealant, the stop bead, the wall and the render.