It'll sound slightly crazy, but I've had friends remove dreadlocks before with this stuff - https://smile.amazon.com/dp/B000A6XGQO/ref=cm_sw_r_awdo_navT_g_5W1DZ72CRT345T4N57AS
I've only used it on horses personally, but I've combed out a lot of burs and extremely tangled manes/tails with it. It does make the hair extremely slippery, and probably isn't curly girl method approved, but it might work well for a one time detangle if it can get dreadlocks out.
One owner of a white golden to another - invest in a bottle of this stuff. After a bath and/or once weekly, spray him down with it. Do it outside since it WILL make your hard flooring extremely slippery (there are literally warnings on to bottle to not spray it where your saddle/girth goes on the horse). If he likes to lay on hard flooring, I'd wait until he's dry to spray him down with it since as he dries it will just get on the floor and still make it slippery.
Next time he goes "mudding" a quick rinse will get 90% off without even needing shampoo. It also will keep his fluff from getting tangled, dry dirt shakes right out, and also makes getting cockleburs and similar stuff out of their coat a piece of cake.
Edit to add: Proof here. Just sprayed him down when we got home - no soap, and took no more than 5 minutes.
Behind the ears is often the most troublesome spot. I’ve found that a couple of detangling products used regularly during brushing makes a huge difference.