(Dow Jones) As Wall Street's signing bonuses for brokers soar ever higher, the strings tying them down are getting thicker.

Recruiting packages are the talk of the industry, with some top advisors now getting ones from the big brokerages that total as much as three times a year's production in fees and commissions from clients.

That means companies won't make a profit on their business for several years. To ensure some eventual return, they insist on building bigger performance hurdles and restrictions into the contracts, which themselves are getting longer.

Upfront bonuses have long been given in the form of a loan that is forgivable over a number of years. If the advisor leaves for another firm during the term of the contract, he or she must pay back a proportionate share of the money.

In the biggest packages, more of the money is coming at the so-called "back end"--that is, not upfront--and is tied to how well the broker performs. They are also dragging out the vesting periods of deferred compensation so brokers will stay put longer.

At about 300% of production, the bonuses are hitting a ceiling, "but they still can be profitable" if the banks structure the deals properly, said Scott Smith, brokerage analyst at Cerulli.

Of course, ceilings are relative. In the mid-1990s, bonuses appeared out of control when they rose to 50% from 25%, triggering a special industry commission, the Tully Commission, to investigate whether investors' interests were being compromised. Seeming to defy business logic, bonuses have continued to rise steadily, dipping only temporarily after the tech stock "bubble" burst in 2001. The 2007 financial crisis only added to incentives as banks, with their other lines of business suffering, were desperate to bring in new client money.

The firms did try to lower signing bonuses at the end of 2009 and in early 2010 but found that brokers refused to move over for less money, said Mindy Diamond, recruiter and president of Diamond Consulting. So the four major firms--Merrill Lynch, Morgan Stanley Smith Barney, Wells Fargo Advisors and UBS Wealth Management Americas--are toughening the structure of the bonuses instead.

"It's not all upfront, it's not all cash, and it's over a nine-year contract," Diamond said. "On the back end, it's more of a performance bonus than a signing bonus."

A few years ago, bonuses were structured with almost all the money in cash up front and just a little extra on the back end. One Merrill Lynch broker, who moved over from UBS in early 2008, recalls his package was relatively simple. "Our deal had practically no performance hurdles attached to it," he said. "Now, all the deals are asset-triggered."