how do i remove poison ivy without making a mess?

Cover everything. Long sleeves, gloves you're happy to bin or heavy rubber ones you wash after, and pull the plants out roots and all after rain when the soil is soft. Bag them straight away. Never burn it - the oil goes airborne in the smoke and that's a lung problem, not a skin one. The oil sticks around on tools and gloves for a long time too, so wash those down with soapy water afterwards and do your clothes in a separate load.