There’s a reason drug dealers store cash in storage units and paint buckets, because it’s not easy laundering money. What could Walter have done? Let’s go through his options one by one:Option 1: Although the The Bank Secrecy Act (1970) requires banks to report transactions above $10,000, Walter could have employed Smurfs (drug mules, but for cash) to make thousands of tiny deposits, which would draw less attention from authorities.Problem: Walter did not have a criminal organization to carry this out. What’s he going to do if a smurf runs off with his money, send Jesse after him with a bong?Option 2: Buy high-ticket items such as vintage comic books or supercars and sell them later.Problem: Similar to the Bank Secrecy Act, businesses have to file a Form 8300, “Report of Cash Payments Over $10,000 Received in a Trade or Business”. Even if those reports don’t alarm the IRS, the large transfers from other people who he would sell the goods would raise red flags, and he’s back to square one.Option 3: Get the money out of the country through casinos or smuggling diamonds.Problem: Even if Walter succeeds in laundering the money while overseas (gamble at a casino and cash out the chips in Macau, for example), he still needs to deposit the clean money at a foreign bank. Unfortunately for Walt, the Foreign Account Tax Compliance Act (2010) requires Americans living outside the U.S. to file yearly reports on their non-U.S. financial accounts to the Financial Crimes Enforcement Network (FINCEN). Banks outside the U.S. are required to fill out a “Know Your Customer” form when you open an account – someone like Walter would immediately raise concerns. This is why many banks in Europe won’t even let Americans open a bank account.Option 4: Invest in the stock market as the OP suggests.Problem: Same thing, any brokerage firm would be obligated to file a Suspicious activity report (SAR) if Walter were to make large deposits that is not commensurate with his income as a high school chemistry teacher.Option 5: Hire a “professional” to do the money laundering, there must be a smart guy who knows how to set up “offshore” bank accounts and stuff.Problem: Money Laundering Control Act (1986) makes money laundering a crime in itself instead of just an element of another crime, so even Saul Goodman would think twice about getting involved with money laundering. And as for finding an export, in 1996, Harvard-educated economist Franklin Jurado was sentenced to 7 1/2 years in prison for laundering $36m for a Colombian cartel.Conclusion: Money laundering was always an afterthought for Walter – he was too busy dealing with the day-to-day stuff of manufacturing and distributing drugs. Walter might have been able to launder that $100m if he had devoted more time and resources into the project, but ultimately, the results might not necessarily be better than burying the money in the desert. His goal was to provide for his family, and barrels of money in the desert does exactly that.—————Edit 1: A few comments have mentioned smuggling the cash (or converted to gold) out to to other countries. I think somehow the idea of the “open sea” implies lawlessness, but it doesn’t. The U.S. Custom and Border Protection has strict Reporting Requirements for pleasure boats, not to mention inspections. If that weren’t the case, people would be smuggling drugs willy-nilly across U.S. borders. However, I’m reminded of the 2001 Movie Heist, starring Gene Hackman as a con-artist. At the very end of the movie, spoiler alert, he took the elicit gold bars, melt them into yacht rails and painted over them, thus avoiding detection.Edit 2: Remi Alaiti pointed out that Saul Goodman did offer to help them launder the money through nail salons (as we know now he got the idea from his Jimmy McGill days), so I stand corrected. However, like the car wash, the nail salon would be too small potatoes to make a significant dent laundering the $80m.Edit 3: As for Bitcoins, it’s less secure than burying money in the desert. See Jonathan Chen's answer to Should I invest in Bitcoin? for details.*I maintain that Walter original purpose for manufacturing meth was to provide for his family, thus the money would’ve had to stay in the country. In time, if his wife and son were on board, they could’ve opened more car washes, nail salons, and other cash-heavy businesses, say, Los Pollos Hermanos franchises, to slowly launder the money.