First, I am not a lawyer.
No-hire and/or non-solicitation clauses can be added to your contract (MSA/PSA). My understanding is they are variably enforceable in different states.
They are generally not enforceable against employees (you are better off developing and maintaining a good relationships with your employees, then trying to force them to do something).
That said, your agreement with your business customers is generally a binding agreement, and should they try to hire your people out from under you, you should have grounds for a lawsuit. Suing your customers has other implications that you may want to consider.
I had a situation where a customer tried to hire one of my employees who had been working on his project for a couple years by that point. He was trying to reduce his expenditures. My employee notified me that this was happening, because we had a good relationship, and I contacted the customer and reminded them of our contract agreements.
This is considered an ethical breach. We weren't providing contract-to-hire headhunter services. Most people who hire vendors understand the distinction, and this customer knew what they were doing (they were being intentionally sneaky about it). At the completion of the contract I fired them as a customer, and moved the employee to another project.

Without having a lot more detail on what you are doing or who your market is, what worked for my company (B2B software professional services) was getting out in front of potential customers by attending trade shows and conference for my target industries, having a booth when I could afford it, speaking about a particularly interesting use-case, do webinars in conjunction with a partner software company and trade associations.
It is hard to stand out when there are a lot of competitors (with a lot more resources) - specializing by technology, solutions, and industry helps you focus on customers who are potentially overwhelmed with options, too.