"I'm not ready for that." is a healthy approach to training things that overwhelm us.
Here are a couple of counters to the standing guard pass to help your game. Years ago I learned the second of these moves at a workshop with Renan Borges. I was still a white belt at the time, and even though I really liked the move, it wasn't something I was ready for.
I filed it away in the "I like this, but I'm not ready for it right now. I'll do my best today, and someday I'll come back to this." A few months ago, it started reappearing in my rolls and here's how I integrated it and hopefully you can too. When you are ready.
Sickle Sweep - place the feet in the hips as they stand up. As they push the leg down, rotate your foot inside to help with leverage. Not necessary, but it can give a good bite on the hip.
Use your other arm to attack the ankle with an underhook. Push up with the foot in the hip, and slice the back of the ankle with your leg as you hold the other ankle.
Deep Pass Defense - when they step through more aggressively, it is difficult to get the leverage to apply the sickle sweep. Here we shoot the arm through the leg following with our head and shoulder. Think of the hand as the tip of the arrow, and the head is the feather.
Place the back of the tricep on the back of the leg to help finish rotating through. No need to pull the leg all the way trhough, and it is faster to use the shin with the other leg. Grab the ankles and leverage up.
You can then take the back, or attack the ankles.