Way back in college, when I actually played at being kinky, my girlfriend and I went to my dad's house to 'visit' we did actually plan to have dinner with him, but we also planned for some private time together as we both lived in dorms at the time.
Dad was supposed to be at work until 5pm, so me and H got busy around lunch. Busy ended up meaning H naked and spread eagled to my rickety old twin bed. At the time, we didn't know stuff like cinch ropes and column ties, I just wrapped and knotted and kept an eye on her fingers and toes to make sure I didn't hurt her.
I was about to finish undressing when we both heard the unmistakable sound of tires on the long gravel driveway to the house. Her eyes got huge at the sound. They got bigger still when I grabbed our agreed upon emergency release, which that day was a wicked sharp hunting knife.
I cut the ropes without cutting either of us. We threw our clothes on and I shoved the ropes under the bed. We got down on the floor and cuddled up, leaning against the wall and some old pillows. We acted like we had been caught making out. It was no chore to look suitably embarrassed, and Dad made no big deal of it. I was such a late bloomer, socially speaking, he was probably glad to see me with an actual girl. The ropes went into a book bag at the first opportunity, and we tried not to look too smug. We didn't think to cover her wrists until later, but if Dad noticed, he kept our secret safe.