Bicycle Mechanics - Chain getting stuck - what to do?

I just installed a new chainring/trouser guard combo on my bike. Today on my commute the chain got derailed and got stuck between the two. The only way to get it out now is to loosen all the chainring bolts.

I'm going to try to figure out why my chain fell off and fix it (I think chain line needs to be adjusted). I'd also like to adjust the distance between the chain ring and trouser guard but I'm not sure which way to go.

Here's my question: Do I try to REDUCE the distance between the chain ring and trouser guard so that the chain won't be able to slip between them, or do I INCREASE the distance so that if the chainring gets derailed at least it won't get stuck?

Likely you need to adjust the front derailleur. I suspect the new crank/chainring/whatever sits just slightly inboard of where the old one was, and now you're "overshifting" onto the big ring.

Adjust the "high" stop screw on your derailleur so that the chain will not be pushed too far and you should be in good shape.

Thanks for response, Bikewer. I have a Schlumpf Mountain Drive instead of a front derailleur (my bike is a Brompton folding bike which does not accommodate a front derailleur). I didn't mention it because my primary question is which way to adjust the distance between the trouser guard and chain ring. I am going to address chain line issue either with bb spacer or chainring bolt spacers and hopefully that will eliminate chain derailing, but I'd still like to ensure that if it ever happens again I don't get stuck on the road because the chain is wedged between the chain ring and trouser guard.

Wow - Kudos to John at Cosmic Wheel in Ridgefield Park, NJ. Took my bike there at lunch time just to get advice and pick up different spacers and tools for my chain ring if necessary. In the middle of a very busy day John took the time to put my bike on his stand, carefully diagnose what was going on and fix it for me right then and there (turned out not only was I able to reduce space between chain ring and trouser guard, but the chain ring itself was slightly bent and needed straightening). Thanks John! I would delete this thread, but since I can't, I figure I may as well give credit to a very helpful LBS.