Here is a little teaser. I try to cut the logest briars I can. To take the thorns off, you can use a knife, or do what I did. Put on a heavy leather glove, grip the briar and slide your hand down it. It will leave little humps where the thorns are.
Once that is done use a small knife to split the stalk. Its easier to split from the big end and work the blade down to the tip.