I cant see getting the blade into your leg, maybe into your foot if you maneuver it wrong. I would get heavy steel toed boots with the additional top instep flap to protect the top of your foot. They tie on with the laces. Other than good eye and hearing protection, that should be all you need if you keep the guards in place.
For cutting vines, saw briars etc. I bought the heavy duty Gator attachment with the 4 steel reversible blades for my weedeater and it works fine. I have the old 4 way skil saw looking blade with 4 notches and the Gator is much better.
Stihl make one with chain saw teeth that they swear cuts 4" saplings but if you have ever used a chainsaw, you know what touching it in the dirt does for instantly dulling the teeth not to mention rocks. Kinda pricey too. I am happy with my less than $15 gator attachment as I have hit rocks and barbed wire with mine and it keeps on ticking like a Timex watch. It is much better than the saw blade style as it is on pivots like a bush hog so if the blade hits an immovable object, they swing back.