Elictrical. Lowes carries the colored electrical tape so you can get one that is at least 'ballpark' to your blank color. I tape a a 3" or so piece over the ferrule running parallel to the blank as a splice, then I spiral over the ferrule and splice piece to lock it all in.
To tape or not? Since spey casts involve a change of direction and lines that are much heavier than their single-hand AFTMA rating equivalents, the torque on the rods is considerable. Scott-type ferrules are said to be more resistant to loosening, but even so... Taping is easy. I use a spiral wrap covering about 1.5 inches on either side of the joint. When not in use, park the tape on the rod blank; you can reuse it at least a half-dozen times.
Out here on the Peninsula, in Port Townsend, there is a company called "Coyote Found Candles". They make a wide range of candles and one of the things they have is a small wax disc, about the size of a silver dollar and about 3/8" thick. It is made of beeswax. It is hard and sticky, but not too dry for ferrules.
It is very handy to use; I make sure the ferrules are clean and dry, then rub the "male" ferrule with the wax disc until it's evenly coated. Then I rub the wax into the surface with my dry finger, rubbing hard enough to create some friction heat to liquify the wax momentarily beneath my finger.
When using wax to add grip to ferrules you have to be careful not to build up too much wax as it can get very hard in cold weather and you might split apart the receiving ferrule with the added diameter caused by the wax.
I have never had a ferrule come apart with this system.
I have had ferrules loosen and once lost a tip on a cast. It didn't go far and was easy to pull in with the line but it scared me. On most rods I will tape, some I get away with just ferrule wax. Since better to be safe than sorry, I usually tape everything.
It does not seem to matter the type of ferrule, some rods loosen and some don't. One thing I have noticed that impacts it is the line and cast. Short bellied lines don't seem to loosen as much as long bellied lines. Also, if I am double, snap-t'ing or single speying, I rarely have a section loosen. If I am throwing a spiral roll (something I do the majority of the time anymore), it really seems to twist them loose.
As for the original question, 3M electrical is the best I have ever found. Supple in alkl bu the coldest weather and leaves no residue.