Via fences or pickets important parameters for design
The short answer is that neither matter in most cases. The only good reason I have for doing such a "fence trace" is to prepare for maybe adding a shielding can later (after testing if it works okay without). The trace in itself does not help much - other than adding some distance (which you could do without the trace).

The longer answer requires you to first explain what you are trying to achieve, why you think this will work and how you think it will work.

In general: If you don't understand what you are doing - maybe don't do it :-) A lot of time is spent copying stuff we "think" is good and often creating more problems than we had in the first place.