Local -
Separating a stuck rod is often difficult because one can't get a straight pull on the rod. Any twist puts pressure on the side making it difficult to pull them apart. Two people working together can often separate the rod easily - stand facing each other put one of your hands on the rod below the joint and the other above. Have your pattern do the same. The result will be straight pull and the rod may easily come apart.

Another trick if you are alone is to place the rod behind your knees with the joint in the center, place hands on opposite sides of the joints and use side pressure from your legs to apply a "straight" pull on the rod.

Neither method are 100% but I have used both many times successfully. I had one rod I could never get apart (glass) and a couple that the only way to separate them was to put the rod outside in a hard freeze (single digits are good). After the rod is throughly chilled quickly warm the outside of the large or female part of the joint with a hair dryer or warm water.

Good luck
Smalma