Intarsia purl

I seem to be able to do intarsia in every scenario apart from when I’m purling and I have a pattern like this:

R2 YXX
R1 YYX
C. 123
But imagine that with the wrong size facing up

Now picture you’re using chunky yarn 12mm needles and you’re on row 2 and it’s time to change from X to Y - how do you trap X ? I don’t know why this is blowing my mind but I can’t do it perfectly normally

Please help

(Help flare said equipment on it)