All sorts of commercial stuff will kill poison ivy, but the easiest to obtain is Roundup. At present, SAMS has a jug with the stuff at 50% solution. The directions list 2.5 ounces per gallon - I use 5 ounces (like Sendero says - the "usual" concentration just kills grass) - put it in a back pack type of sprayer (mine holds 4 gallons), and walk around your property coating (not just a spritz) all poison ivy, prickly vines (wild raspberry/blackberry in my area) and the like you wish to eradicate. WATCH out and don't spray the stuff you wish to save (including the trunks of any trees that don't have a good covering of bark).
I just got through doing such on my property this weekend. The task was about 25% of what I needed last year, and 10% of the first year I walked around my 7.5 acres (I spent 2 days and 6 jugs, at $47 per jug, of 50% Roundup the first year). So, some poison ivy or other noxious stuff will survive one coating, but the second year - you zap what's left - I'm now on the third year (yup, in SC I've got fire ants - Amdro via a broadcast spreader once a year has taken care of most, and spot applications on mounds thereafter controls things).
So, I can now have a party on the property, with city folks wandering around with glasses of wine/beer all afternoon (and by the end of the afternoon, no one recognizes poison ivy or a fire ant mound, if they knew what one was in the first place), or kids chasing squirrels, and there will be few, if any, rashes or bites as souvernirs.
