From Foxsports.com:

Reds left fielder Adam Dunn lacks a no-trade clause, but his contract includes a provision that grants him his own form of protection, effectively allowing him to determine his own fate.
If Dunn is traded, his $13 million club option for ’08 will be voided, making him a free agent at the end of the season, according to a source with knowledge of his contract.

Thus, any team that acquired him likely would request a negotiating window to sign him long-term, rather than simply rent him for two or three months.

If the Reds keep Dunn and exercise his option after the season, he will gain full no-trade protection until next June 15. After that date, he could be traded to 10 clubs, but the list would be of his own choosing.

Very interesting contract by Dunn’s agent. It essentially makes him difficult to trade before the deadline as I would think an extension of the size we’re talking about would be difficult to work out within that window.

And if the Reds don’t trade him before the end of the season, he’d be very difficult to trade next year, as he has control over the process.