I've usually used a double uni-knot to join lines. However, when I've done this with braid on heavy fluorocarbon, the braid tends to dig into the fluorocarbon and eventually cuts the loop with enough pressure applied.

I switched to an Alberto knot which works great, except for one thing: the knot is so large (joining 80 lb leader to 60 or 80 lb braid) that it can't easily pass through the last line guide. Is there a more "compact" knot that avoids the braid loop cut problem while being sufficiently small to pass through the line guides, as double-uni knots do?

FG knot

Look for the salt strong video on YouTube

Thanks, I'll give it a try. Looks like it requires a lot more effort and dexterity than the Alberto, but may be worth it if I can get a slim knot with the same strength.

FG Knot. very strong, easy to tie. or you can do the Double Uni knot, but the FG is a lot better IMO.

Try a surgeon's knot. Easy to tie, never had any trouble with one slipping.