The vine (in the pictures) growing on your fence is not poison ivy, it is pepper vine (Ampelopsis arborea) and the foliage is not poisonous. If Roundup has not been successful, try an herbicide with the active ingredient triclopyr. It can be applied to the foliage to knock it down. The best practice is to cut the base of the vine, about 10" off the ground and paint the fresh cut with the herbicide to keep it from growing back. Please read and follow all label directions.https://aggie-horticulture.tamu.edu/newsletters/hortupdate/2008/jan08/Peppervine.html

https://plants.ces.ncsu.edu/plants/ampelopsis-arborea/

Thanks for the question.

Thank you for your quick reply.  The weed that seems to be the problem is not dark green in the beginning.  It is skinny and sprouts a reddish color--turning a  darker green as it ages.  It has leaves of three sprouting off the stem.  Is that not poison ivy?  My grandson breaks out in a really bad rash every time he mows the back yard.  It sprouts up all over the place--in the middle of the yard, along the fence line.   My neighbors have told me it is also showing up in their yards for the last few years, too. None of us have had much luck in getting rid of it.    Since I have gotten too old to work on the yard myself, and certainly my grandson can't manage it, how do I locate a service (if such a thing exists) to treat it?   I am sending different pictures.

Pepper vine. See this link. https://www.lsuagcenter.com/~/media/system/5/3/d/7/53d736a39e4112886d62c5ed2d273fb8/ne%20region%20horticultre%20volume%201%20issue%202pdf.pdf

Thanks