This ability doesn't really work: it's a rule-setting ability (so it doesn't lock onto the its affected subjects), and after combat--when there's no such notion as an attacking creature anymore--the effect wears off. Basically, all it does as written is cause your opponent's creatures to lose first strike unless they're blocking this.

Oh, and without a duration, it will apply its (minimal) effect to whatever other creatures may attack for you in future turns, even if this is no longer around. That would be annoying to bookkeep for.

The cleanest wording that does what you're probably aiming for is "Whenever ~ attacks, other creatures you control are indestructible until end of turn."

This is more of a placeholder card, a rough idea, but thanks for the comment; you're right I hadn't even thought about all that haha.