this is just a hunch ,
we MUST use in if we're talking about something specific, a certain field/place/etc
but if it's gerund or activity or action, like in the first post "making dec.." which is a gerund, then it's up to you , if you see making dec as a "particular Field of expertise" then you use IN , if you see it only as an activity then you can omit the in .
Like this :
Activity, not a specific field : reading, writing, watching tv
specific field : landscaping, modeling<the modeling business>, etc
just guessing after saying the sentences out loud ....silly me
Beavercanal Land English Community