You know those invisible electronic fences designed to shock a pet that tries to stray from the yard? Eventually, you can unplug the system, because the pooch knows where not to go.

Philadelphia's campaign finance limits are a little like that. For years, city officials have accepted political contributions only within the limits because they thought they had to. Turns out there was no juice in the fence.

City Councilman Bill Green showed us in his 2012 campaign finance report that he could and did legally accept $30,000 from a single donor -- bottling company owner Harold Honickman. Councilman Bobby Henon figured it out, too, and took three contributions totalling $24,000 from the political committee of Local 98 of the International Brotherhood of Electrical Workers, his former employer.

Green and Henon could do that because the donation limits ($2,900 a year for individuals, $11,500 for committees) apply only to candidates for office; technically, neither is running at the moment. A little-noticed city Board of Ethics opinion from early 2011 confirms elected officials can wander right past the fence if they want to.

Kenney, Green both have campaign finance bills

Jim Kenney saw my story from Monday and within three days has proposed a legislative solution -- a bill that requires city elected officials to abide by the contribution limits while in office, period.

One obvious issue here is that people who aren't city office holders aren't restricted to the limits, and thus have at least a theoretical advantage over incumbents they might want to challenge.

Kenney acknowledged that, but added, "We have an advantage as incumbents, of getting free press, and being in the public eye and having a public office and serving people."

I asked Green what he thought of Kenney's bill. "I'll reserve judgment until I see what he's trying to do, and maybe I'll be supportive of it," he said. Hmmmm.

Meanwhile Green introduced a campaign finance bill of his own attacking another issue -- the prospect that independent committees might spend big money to support or attack a candidate in a city election and not have to disclose their contributors or spending.

"We believe that there's a constitutional way to require disclosure basically about the same time that spending occurs, so voters will know whose money is influencing the election," Green said.

So Green's bill requires disclosure within five days of any expenditure of $100 or more.

 You can read Kenney's bill here, and Green's here.