The second- and third-floor parking levels of the Indianapolis Public Schools headquarters will remain surrounded on three sides by a chain-link fence at least until the spring, a school district official said today. The unsightly fence will come down next year, but it isn't clear yet what will replace it. The limestone that previous hid the parking levels was removed so workers could shore up the structure. Replacing the stone could be prohibitively expensive for the financially strapped school district, adding another $1 million or more to the $2.3 million project. Any ideas for what they could do?