Drill into it with a larger wood bit to make tunnels about quarter to half inch deep - depending on the size of the stump, put them at regular intervals. Fill the tunnels with SBK (brushwood killer) and cover with something. Don't spill it on the soil, wear gloves.

dont mention tree stumps to me lol, ive just taken 3 and one to go,,, out, a nightmare, im removing as i want to plant a new area, i left a tree stump in another part of my garden last year and could just about grow some shallow planting because of roots everywhere, but bamboo is right if you arent going to plant anything there

Or even if you are - no problem with planting around it as long as the SBK's not been spilt on the ground.