You probably understand wrongly (you should not wrap a GPL program with some protocol to communicate with a proprietary software without great cautions), and you should contact your lawyer, or the FSF.
I am not a lawyer, but my understanding is that if you design a specific protocol to communicate (from some GPL program) with only a proprietary process it is legally a linking or a derived work (license-wise, linking is not restricted to use
ld). Things could be different if you have a public and documented protocol communicating with several programs, one of them being GPL.
In some legal systems, the court will evaluate if your intent was to hijack the spirit of GPL. You really need a lawyer and or the advice of FSF.
Did you consider publishing your application as free software under a GPL compatible license (You can commercialize GPL software, provided you give access to the source code under GPL license)?
And please, read more about free software. The goal of free software is not to assist proprietary developers (but to give freedom to users). Please visit the https://www.fsf.org/ site
You are probably considering making a huge mistake; are you sure to want to violate (or even to risk violating) the GPL license or its spirit? your career, your reputation, your employer & clients could suffer (e.g. financial loss, or even go to jail in some countries); at your place I would not risk doing what you want to do (unless covered by a lawyer, who will defend you in court)!
BTW, the whole point is understanding what "communicate at arms length" means, and you probably need a lawyer for that.