Be honest, did you?
Hidden away in the depths of your iPhone's settings is the ability to fiddle with the duration of your audio and video messages, allowing them to "self destruct" after a set amount of time.
Here's how to give them a tweak.
First up, you'll want to click the Settings cog
From here, scroll down until you find Messages
All the way down at the bottom of the Messages section is the ability to play around with the Expiry settings of audio and video messages.
You can either ensure that media messages never disappear, or set them to expire after two minutes, at which point they'll no longer take up storage in your message chain. So long as you send either audio or video as a direct message (rather than an attachment), it'll disappear after two minutes with this setting turned on.
Sure, it's not quite as secure as Snapchat, but it's a neat tool for any clandestine requirements you might have.