Here is a system utilizing two of the three dozens/columns, that hopefully has never been posted before. It shows promise but is somewhat of a grind.

Wagers are based on the dozens or columns from the last two spins.

You might find it helpful to track the spins in terms of dozens or columns, rather than numbers. I use letters for the dozens (A,B,C) and numbers for the columns (1,2,3). For example, 7 is A1, 23 is B2, 30 is C3 and so forth.

The trigger appears when the two spins come from the same dozen, but different columns, or the same column, but different dozens (for example, A1 & A3 or B2 and C2). If any other result appears, like A1 & B2, or A1 & A1, wait for the next spin to see if the trigger appears before placing a wager.

Assuming the trigger appears, start by placing one unit on each of the two different dozens/columns. Increase the wager by one unit only if both wagers lose. Reset the wager to one unit upon equaling or exceeding the previous high, which means we must track both the bankroll amount as well as the dozen/columns.

If 0 or 00 appears, wait for the next two spins to see if the trigger appears.

Here is an example of 35 spins, taken from a RNG, starting with a ten unit bankroll.

B1

C3

A3---1 unit on the first and third dozen

A1---win, bankroll = 11, 1 unit on the first and third column

B1---win, bankroll = 12, 1 unit on the first and second dozen

A2---win, bankroll = 13, wait for next trigger

C1

B2

C1

B2

B2

A3

A2---1 unit on the second and third column

00---loss, bankroll = 11, add 1 unit after trigger appears

B2

B1---2 units on the first and second column

C1---win, bankroll = 13, = previous high, reset to 1 unit on second and third dozen

C2---win, bankroll =14, 1 unit on the first and second column

B1---win, bankroll = 15, wait for next trigger

C1---1 unit on second and third dozen

A1---loss, bankroll = 13, 2 units on first and third dozen

00---loss, bankroll = 9, add 1 unit after trigger appears

B1

C3

A1

A3---3 units on first and third column

C1---win, bankroll = 12, continue with 3 unit wager when trigger appears

B3

C1

C1

C3---3 units on the first and third column

C2---loss, bankroll = 6, add 1 unit, 4 units on second and third column

B2---win, bankroll = 10, 4 units on the second and third dozen

C2---win, bankroll = 14 units, have not matched or exceeded previous high, 4 units on second and third dozen

C2---win, bankroll = 18 units, reset to 1 unit when trigger appears